0% APR purchase cards — how interest-free financing really works

A zero-percent annual percentage rate on new purchases is, at its core, a short-term interest-free loan from a credit card issuer to a cardholder. The issuer agrees not to charge interest on purchases made during a promotional window — typically 12 to 21 months from account opening — in exchange for acquiring a new customer who will, the issuer hopes, continue using the card (and paying interest on a revolving balance) long after the promotional period expires. The cardholder, if disciplined, can use the same window to finance a large planned purchase without paying a cent of interest, or to hold onto cash that would have been spent and earn a return on it in a savings account or short-term Treasuries while making fixed monthly payments toward the promotional balance.

The structure is one of the most consumer-favorable features in the US credit card market, and also one of the most frequently misunderstood. The misunderstanding runs in two directions. First, many cardholders do not distinguish between waived interest (what most bank-issued 0% APR cards offer) and deferred interest (what most store-branded financing offers impose) — a distinction that can cost hundreds or thousands of dollars if the balance is not fully paid by the deadline. Second, many cardholders treat the 0% promotional window as permission to spend more rather than as a financing tool for a purchase they would have made anyway, which converts the interest-free loan into a trap that delivers the cardholder to the post-promotional APR carrying a balance they did not plan for and cannot quickly pay down.

This guide covers how 0% APR promotional periods work mechanically on new purchases, the critical distinction between deferred interest and waived interest, the opportunity-cost math that makes 0% APR a genuine arbitrage for disciplined cardholders, how the grace period interacts with promotional rates, what happens when the promotional window closes, the payment strategy that guarantees the balance is paid before the cliff, the risks that undermine the strategy, the specific use cases where 0% financing is most valuable, and the Consumer Financial Protection Bureau’s warnings about store-card deferred interest.

How 0% APR promotional periods work on new purchases

When a credit card issuer advertises “0% APR on purchases for 18 months,” the offer means that any purchase made during the promotional window will not accrue interest from the transaction date through the end of the promotional period, provided the cardholder makes at least the minimum payment each month. The promotional period starts on the date the account is opened (not the date the card arrives in the mail, though in practice these are usually close), and it ends on a specific date disclosed in the cardmember agreement — typically expressed as “the end of your 18th billing cycle.”

The mechanics are governed by the Credit Card Accountability Responsibility and Disclosure Act of 2009, which requires issuers to disclose the promotional rate, the duration of the promotion, and the rate that will apply after the promotion ends, in clear language and in a standardized format (the Schumer Box) that appears before the applicant submits the application. The CARD Act does not regulate the length of the promotional period or the post-promotional rate; it regulates transparency.

The 0% rate applies only to purchase transactions. Cash advances, balance transfers, convenience checks, and other non-purchase transaction types carry their own rates and are not covered by a purchase-APR promotion unless the offer explicitly states otherwise. Balance transfers on the same card are sometimes covered by a separate 0% promotional rate with its own window length and fee structure — the mechanics of balance transfer promotions are covered in the balance transfer mechanics guide — but the two promotions are independent. A cardholder who has 0% on purchases for 18 months and 0% on balance transfers for 15 months will see the balance transfer rate expire three months before the purchase rate, and any remaining transferred balance will start accruing interest at the post-promotional balance transfer APR while the purchase balance remains at 0%.

During the promotional period, the cardholder must make the minimum payment each billing cycle. The minimum payment on a 0% balance is typically either a flat dollar amount (often $25 or $35) or 1% of the balance, whichever is greater. Making the minimum payment keeps the account current and preserves the promotional rate. Missing the minimum payment gives the issuer the contractual right to revoke the promotional rate and move the entire balance to the standard purchase APR.

One feature that surprises many cardholders: purchases made after the promotional window closes — even on the same card — accrue interest at the standard purchase APR from the date of the transaction, with the grace period operating normally (provided the full statement balance is paid by the due date). The promotional rate is not a permanent feature of the account; it is a time-limited acquisition incentive.

Deferred interest versus waived interest — the distinction that costs people money

This is the single most important distinction in promotional-rate financing, and it is the distinction most consumers fail to make. The two structures look identical from the front — both advertise “0% interest for 12 months” or similar language — but they produce radically different outcomes when the balance is not fully paid by the end of the promotional period.

Waived interest is the structure used by most bank-issued general-purpose credit cards (Chase, Citi, Capital One, American Express, Discover, Bank of America, Wells Fargo, U.S. Bank). Under the waived-interest structure, interest is genuinely not charged during the promotional period. When the promotional period ends, interest begins accruing on the remaining balance from that date forward at the post-promotional APR. If the cardholder has a $3,000 balance at the end of a waived-interest promotional period and the post-promotional APR is 24%, interest accrues on $3,000 starting the day after the promotional period expires. There is no retroactive interest charge for the months during the promotional period.

Deferred interest is the structure used by most store-branded credit cards and retail financing plans — the kind offered at furniture stores, appliance dealers, dental offices, jewelry retailers, and electronics chains. Under the deferred-interest structure, the issuer calculates interest on the original purchase amount from the date of purchase for the entire promotional period, but defers the charge — holds it in a pending state — contingent on the cardholder paying the full balance before the period expires. If the cardholder pays the full balance before the deadline, the deferred interest is waived and the cardholder pays nothing beyond the purchase price. If the cardholder fails to pay the full balance — even by one dollar — before the deadline, the entire deferred interest charge is added to the account retroactively.

The numerical difference is severe. Consider a $4,000 furniture purchase financed at “0% for 12 months” under a deferred-interest plan at 29.99% APR. The cardholder makes minimum payments of approximately $100 per month for 11 months, paying down $1,100 of the balance. At the end of month 12, the remaining balance is $2,900. Because the cardholder did not pay the full $4,000 before the deadline, the deferred interest — calculated at 29.99% on the original $4,000 from the date of purchase for 12 months — is approximately $1,200. That $1,200 is added to the $2,900 remaining balance, creating a total balance of $4,100 — more than the original purchase price — now accruing interest at 29.99% going forward.

If the same $4,000 had been financed on a waived-interest bank credit card, the cardholder in the same position (with $2,900 remaining at the end of the promotional period) would owe exactly $2,900, and interest would begin accruing only from that date forward. No retroactive charge. The difference between the two outcomes — $4,100 versus $2,900 — is $1,200, which is exactly the retroactive interest the deferred-interest structure imposes.

The Federal Trade Commission and the Consumer Financial Protection Bureau have both published consumer advisories specifically about deferred-interest plans. The CFPB’s 2014 report on the store credit card market found that a significant percentage of consumers who opened deferred-interest accounts did not pay the full balance before the promotional period ended and were charged the retroactive interest. The structure is legal, clearly disclosed (in the fine print), and extremely profitable for the issuers who use it — which is why it persists.

Which cards offer the longest 0% windows — and what to look for

The US credit card market in 2026 clusters around four standard promotional-window lengths for 0% APR on new purchases: 12 months, 15 months, 18 months, and 21 months. A small number of credit union products extend to 24 months, but these are typically limited to members of specific credit unions and are not widely available through general application channels.

The longest promotional windows tend to come from large national issuers competing aggressively for new cardmembers. As of early 2026, several well-known products offer 15 to 21 months of 0% APR on purchases: the Wells Fargo Reflect, the Citi Simplicity, the U.S. Bank Visa Platinum, and similar products. The specific offers rotate — issuers periodically adjust the window length as a competitive lever — so the specific card names are less important than the evaluation framework.

When comparing 0% APR purchase offers, four variables matter beyond the headline window length:

Post-promotional APR. This is the rate that applies to any remaining balance after the promotional period. The range across issuers is 18% to 29%, and the rate is usually variable (indexed to the prime rate). A 21-month 0% offer with a 27% post-promotional rate is less forgiving than an 18-month 0% offer with a 20% post-promotional rate if the cardholder does not pay off the balance in time. The post-promotional rate is the price of failure; evaluating the offer without evaluating the failure case is incomplete.

Annual fee. Most 0% APR purchase cards carry no annual fee, which is structurally important because the value proposition is a temporary financing benefit, not an ongoing rewards program. A card that charges a $95 annual fee for the privilege of 0% APR on purchases for 18 months is reducing the effective interest-free benefit by $95 — which on a $3,000 balance is equivalent to adding about 3.5% to the interest rate. Avoid annual fees on 0% APR cards unless the card also carries rewards that independently justify the fee.

Rewards during the promotional period. Some 0% APR cards also earn cash back or points on purchases made during the promotional window. A card that offers 0% APR for 15 months and also earns 1.5% cash back on all purchases is structurally better than one that offers 0% for 18 months with no rewards, if the cardholder intends to pay the balance in full within 15 months regardless. The three additional months of 0% are irrelevant if the balance is gone by month 15, but the 1.5% cash back on $5,000 of purchases is $75 of additional value. The evaluation should consider both the financing benefit and the ongoing earn rate.

Credit requirements. Most 0% APR promotional offers are available to applicants with good to excellent credit — generally a FICO score of 670 or higher, with the longest windows (18-21 months) typically requiring 720 or higher. A cardholder with a 650 FICO score may be approved for a shorter promotional window (12 months) or may not receive the promotional rate at all, receiving instead the standard purchase APR from day one. The promotional rate is not guaranteed at application; it is contingent on the issuer’s underwriting decision.

The opportunity-cost math — 0% APR as an interest-free arbitrage

The most financially literate use of a 0% APR purchase card is not to finance a purchase the cardholder cannot afford — it is to finance a purchase the cardholder can afford to pay in cash, but chooses to finance at 0% while the cash earns a return elsewhere. This is a straightforward arbitrage: borrow at 0%, invest at a positive rate, pocket the difference.

The math on a worked example. A cardholder plans to buy a $6,000 appliance package for a kitchen renovation. The cardholder has $6,000 in a checking account and could pay cash. Instead, the cardholder applies for a 0% APR purchase card with an 18-month promotional window, charges the $6,000, and places the $6,000 in a high-yield savings account earning 4.5% APY.

The cardholder sets up a fixed monthly payment of $353 ($6,000 divided by 17 months, using a one-month buffer for safety) against the 0% balance. Each month, $353 leaves the savings account and goes to the credit card payment. The savings account balance declines over the 18 months as payments are made, but the balance earns interest throughout.

The approximate interest earned over the 18 months, accounting for the declining balance as payments are drawn: approximately $230 to $260, depending on the exact compounding and the month-to-month balance curve. That is $230 to $260 of free money — interest the cardholder earned on cash that would have been spent on day one if the cardholder had paid with a debit card or check.

The arbitrage works because the promotional rate is genuinely zero — there is no fee to finance purchases at 0% APR (unlike a balance transfer, which typically carries a 3-5% fee). The cardholder borrows at 0% and earns at 4.5-5.0%. The only requirement is discipline: the cash must stay invested and available for the monthly payments, and the entire balance must be paid before the promotional period ends. A cardholder who diverts the $6,000 to another purpose — a vacation, another purchase, a speculative investment — and then cannot pay the credit card balance when the promotional period expires will face the post-promotional APR on the remaining balance, which will rapidly erase the $245 of earned interest and then some.

This strategy is the inverse of the minimum-payment trap documented in the minimum-payment math guide. Where the minimum-payment structure works in the issuer’s favor by extending the repayment timeline and maximizing interest paid, the 0% APR arbitrage works in the cardholder’s favor by compressing the repayment into the interest-free window and capturing the time value of money during that window.

How the grace period interacts with 0% promotional periods

The interaction between the standard grace period and a 0% promotional APR is a source of confusion for many cardholders, because the two features serve overlapping but distinct functions.

During the 0% promotional period, the grace period is largely academic for purchases covered by the promotion. The cardholder is already not paying interest on those purchases because of the promotional rate, so the grace period’s interest-free window does not provide additional benefit. The promotional rate overrides the need for the grace period on promotional purchases.

However, the grace period becomes relevant in two specific situations during the promotional period.

First, if the cardholder also uses the card for purchases that are not covered by the promotional rate — either because the promotional window has partially expired (some offers cover only purchases made in the first few months, not purchases made throughout the entire promotional window) or because certain transaction types are excluded from the promotion — the grace period determines whether those non-promotional purchases accrue interest.

Second, the grace period becomes critically important when the promotional period ends. On the day the promotional rate expires, the card reverts to the standard purchase APR. From that point forward, the grace period operates normally: if the cardholder pays the full statement balance (including any remaining promotional balance) by the due date, new purchases do not accrue interest. If the cardholder carries a remaining promotional balance past the first post-promotional due date, the grace period is lost on new purchases, and every subsequent purchase accrues interest from the date of the transaction.

The practical implication: a cardholder who finishes the promotional period with a remaining balance should stop making new purchases on the card immediately. Using the card for new purchases while carrying a post-promotional balance means paying interest on those purchases from day one, with no grace period, at the standard 20-29% APR. The card becomes one of the most expensive payment methods available until the balance is fully cleared and the grace period is restored — which requires paying the full statement balance for two consecutive billing cycles.

What happens when the promotional period ends

The transition from 0% to the post-promotional APR is the most dangerous moment in the lifecycle of a promotional purchase card. The mechanics are simple but the consequences are sharp.

On the first day after the promotional period expires, the remaining balance begins accruing interest at the post-promotional purchase APR. This rate is disclosed at application (in the Schumer Box) and is typically 20-29% variable, indexed to the prime rate. The interest is calculated using the average daily balance method: the issuer sums the daily balance for each day of the billing cycle, divides by the number of days in the cycle, and multiplies by the daily periodic rate (the APR divided by 365).

A worked example of the cliff. A cardholder has a $4,200 remaining balance when the 18-month promotional period ends. The post-promotional APR is 24.99%. The cardholder continues making payments of $200 per month.

In the first month after the promo ends, interest accrued on the $4,200 balance is approximately $87 ($4,200 times 24.99% divided by 12). Of the $200 payment, $87 goes to interest and $113 goes to principal, leaving a balance of approximately $4,087. In the second month, interest is approximately $85, principal reduction is $115, balance is $3,972. The amortization at this rate means the $4,200 balance takes approximately 25 months to pay off at $200/month, during which the cardholder pays approximately $875 in total interest.

Had the cardholder increased the monthly payment during the promotional period from $200 to $250, the balance at the end of the 18-month window would have been approximately $3,300 — and the total post-promotional interest on $3,300 at the same rate and payment would be approximately $580. The $50/month increase during the promotional period would have saved approximately $295 in post-promotional interest. This is the leverage effect of the promotional window: every additional dollar paid during the 0% period avoids interest at the post-promotional rate, which makes the effective return on accelerated payments during the 0% window equal to the post-promotional APR.

Payment strategy during the 0% period

The optimal payment strategy during a 0% promotional period is mechanical and should be set up on autopay from the day the first statement is generated.

Step one: calculate the fixed monthly payment. Take the total balance (including any balance transfer fee if a balance transfer is also involved, though pure purchase promotions do not carry a transaction fee) and divide by the number of months in the promotional period minus one (the one-month buffer). On a $5,400 balance with a 15-month promotional window: $5,400 / 14 = $386 per month. Round up to $390 for clean math.

Step two: set autopay to that fixed amount. Do not set autopay to the minimum payment. The minimum payment on a $5,400 balance at 0% is typically $54 to $75 per month. If the cardholder pays only the minimum for 15 months, the total paid is approximately $810 to $1,125, leaving a remaining balance of $4,275 to $4,590 — which then starts accruing interest at the post-promotional rate. The minimum payment is the issuer’s preferred outcome; it delivers the cardholder to the post-promotional rate with the largest possible remaining balance. The fixed-payment autopay is the cardholder’s defense against that outcome.

Step three: do not use the card for new purchases. This is the discipline requirement. Every new purchase added to the card during the promotional period increases the balance that must be paid off before the window closes. A cardholder who finances $5,400 at 0% and then adds $2,000 of new purchases during the promotional period now needs to pay off $7,400 in 14 months — $529 per month instead of $386. If the cardholder does not adjust the payment upward, the additional purchases push the payoff past the promotional window.

The exception: if the card also earns rewards on purchases (cash back, points), the cardholder may choose to use the card for everyday purchases and pay those purchases off separately each month while also making the fixed payment toward the promotional balance. This requires careful tracking — the cardholder must ensure that monthly payments cover both the fixed promotional paydown and the full amount of new purchases — but it captures both the 0% financing benefit and the ongoing rewards. The tracking complexity makes this approach suitable only for cardholders who monitor their statements monthly.

Risks — overspending, the deadline, and the minimum-payment trap

Three behavioral risks undermine the 0% APR strategy more often than any mechanical failure.

Risk one: the spending expansion. A 0% APR card creates a psychological permission structure. A cardholder who planned to buy a $2,000 laptop finances it at 0% — and then adds a $600 monitor, a $400 keyboard-and-accessories package, and a $300 software subscription, because “it’s all at 0%.” The $2,000 planned purchase has become a $3,300 total balance. The required monthly payment to clear $3,300 in 14 months is $236/month. The cardholder budgeted for $143/month ($2,000 / 14). The gap between the planned payment and the required payment is $93/month, which the cardholder either covers by cutting other spending or does not cover, in which case the balance is not paid off before the promotional period ends. The 0% rate enabled spending that would not have occurred at the standard APR, and the resulting balance may end up costing more in post-promotional interest than the interest saved during the promotional window.

Risk two: the deadline drift. The promotional period expires on a specific date, but many cardholders do not track that date. The expiration is disclosed on the original cardmember agreement and is sometimes printed on monthly statements, but it is not prominently featured in the card’s mobile app or online portal. A cardholder who opened the card in January 2026 with an 18-month promotional period needs to have the balance paid in full by approximately July 2027. By month 12, the cardholder has settled into a payment routine and may have forgotten the exact expiration date. A surprise expense in month 16 disrupts the payment plan, and the cardholder discovers in month 18 that a $1,200 balance remains — now accruing interest at 24%.

The defense: set a calendar reminder for three months before the promotional period ends, with the remaining balance and the monthly payment needed to clear it in the remaining months. Adjust the autopay amount if necessary.

Risk three: the minimum-payment default. This is the issuer’s structural advantage. The minimum payment on a 0% balance is small — intentionally so. The issuer benefits if the cardholder pays only the minimum during the promotional period, because the largest possible balance then transitions to the post-promotional APR. The CARD Act requires issuers to disclose on each statement how long it would take to pay off the balance at the minimum payment and how much total interest would be paid, but during the 0% period those disclosures show artificially favorable numbers (because the current rate is 0%) that do not reflect what will happen after the promotion expires. The minimum-payment disclosure during the promotional period is not a useful planning tool; the cardholder needs to project the post-promotional scenario independently.

The full mechanics of how minimum payments are calculated, why they extend repayment timelines, and how the CARD Act disclosures work are covered in the minimum-payment math guide.

0% APR for large planned purchases — when the strategy works best

The 0% APR purchase card is most valuable as a financing tool for large, planned, one-time purchases that the cardholder would make regardless of the financing terms. The three categories where the math is most favorable:

Home furnishings and appliances. A kitchen renovation, a living room furniture set, a washer-dryer pair — purchases in the $2,000 to $10,000 range that the household needs to make and can pay for over 12 to 18 months without financial strain. The 0% card allows the household to spread the cost over the promotional window while keeping the cash in a savings account earning interest. On a $7,000 appliance package financed at 0% for 18 months while the cash earns 4.5% in a high-yield savings account, the household earns approximately $280 in interest — a meaningful offset against the purchase price, equivalent to a 4% discount on the appliances.

The critical point: the household should not use a store-branded credit card for this purchase unless they are certain they can pay the balance in full before the promotional deadline. Store cards almost universally use the deferred-interest structure, which means a remaining balance of even $50 on a $7,000 purchase at 29.99% would trigger approximately $2,100 in retroactive interest. A bank-issued 0% APR card with the waived-interest structure is the safer vehicle, even if the promotional window is slightly shorter.

Medical expenses. Medical billing in the United States frequently involves negotiation, payment plans, and interest-bearing financing offered by the provider or a third-party medical financing company (CareCredit, Prosper Healthcare Lending). These financing plans often use deferred-interest structures with short promotional windows (6-12 months) and high post-promotional APRs (26.99% is standard for CareCredit). A cardholder who instead charges the medical expense to a 0% APR bank-issued card with an 18-month waived-interest window has a longer repayment period, a safer interest structure, and — if the card earns rewards — cash back on the medical spend that partly offsets the cost of care.

Planned technology purchases. A laptop, a home office setup, a major electronics purchase — items in the $1,500 to $4,000 range that the household plans to buy and can pay off within the promotional window. The 0% financing eliminates the need to draw down an emergency fund or liquidate an investment for a planned purchase, preserving financial flexibility.

The common thread: the purchase is planned, the amount is known in advance, the household can sustain the required monthly payment, and the 0% card is selected specifically for the purchase rather than used opportunistically after the purchase is already made.

Store cards with deferred interest — the CFPB warning

The Consumer Financial Protection Bureau has published multiple reports and consumer advisories about deferred-interest financing plans, most recently in its ongoing monitoring of the store credit card market. The CFPB’s findings are consistent and concerning.

Store-branded credit cards — the kind offered at checkout by furniture stores, electronics retailers, jewelry chains, home improvement stores, and medical financing providers — are the primary vehicle for deferred-interest financing in the US market. The CFPB’s data shows that these cards carry higher APRs than general-purpose bank cards (the median store card APR exceeds 28%, versus approximately 22-24% for general-purpose cards), and that a significant share of consumers who open deferred-interest accounts do not pay the full balance before the promotional period expires, triggering the retroactive interest charge. The exact mechanics, with a worked amortization example showing how a small leftover balance detonates a full retroactive bill, are covered in the dedicated deferred-interest “same as cash” guide.

The marketing of these cards compounds the problem. The promotional offer is typically presented at the point of sale — at the furniture store checkout, in the dental office billing department, at the electronics counter — when the consumer has already decided to make the purchase and is focused on completing the transaction, not on evaluating financing terms. The salesperson emphasizes “no interest for 12 months” without explaining that the offer is a deferred-interest plan, that interest is calculated retroactively from the purchase date, and that any remaining balance at the end of the promotional period triggers the full retroactive charge.

The defensive posture for consumers considering a large purchase with promotional financing: if the retailer offers “0% interest if paid in full within 12 months,” assume it is a deferred-interest plan unless the cardmember agreement explicitly states otherwise. Compare the store card’s offer against a bank-issued general-purpose 0% APR card. The bank card will almost certainly offer a longer promotional window (15-21 months versus the store card’s typical 6-12 months), a waived-interest structure (no retroactive charges), a lower post-promotional APR, and potentially cash back or points on the purchase. The store card’s only advantage is immediacy — it can be opened and used at the point of sale — but that advantage is also its danger, because it compresses the evaluation window from days to minutes.

If the only option is the store card, the cardholder should treat the deferred-interest deadline as an absolute constraint. Calculate the required monthly payment to clear the full balance at least one month before the deadline. Set autopay. Do not add new purchases to the card. Track the deadline with a calendar reminder. And understand that the penalty for missing the deadline is not a late fee or a ding on the credit report — it is hundreds or thousands of dollars in retroactive interest, calculated on the original purchase amount from the date of the transaction, at a rate that typically exceeds 28%.

Combining 0% APR with sign-up bonuses — stacking the value

Some 0% APR purchase cards also carry a sign-up bonus — a one-time cash back or points award for meeting a minimum spending requirement in the first three to six months. When the two features align on the same card, the cardholder can stack the value: finance a large purchase at 0%, meet the minimum spending requirement with the same purchase, and collect the sign-up bonus on top of the interest-free financing.

A worked example: a card offers 0% APR on purchases for 15 months, 2% cash back on all purchases, and a $200 sign-up bonus for spending $1,500 in the first three months. The cardholder finances a $5,000 purchase at 0% and earns $200 (sign-up bonus) plus $100 (2% cash back on $5,000) = $300 in total card rewards, while also earning approximately $175 in interest from the cash held in a high-yield savings account during the 15-month payoff period. Total benefit: $475 for using the card instead of paying cash — on a purchase the cardholder would have made regardless.

The evaluation framework for sign-up bonus math — including the minimum spending requirement, the conservative point valuation, and the year-one effective yield — is covered in the sign-up bonus math guide.

The stacking strategy requires the same discipline as the standalone 0% strategy: the balance must be paid in full before the promotional period ends, and the sign-up bonus should not be treated as incentive to increase the purchase amount beyond what was already planned.

The bottom line — when 0% APR is a tool and when it is a trap

A 0% APR purchase card is one of the few genuinely consumer-favorable features in the US credit card market. Unlike rewards programs, which are funded by interchange fees that merchants ultimately pass through to all consumers in higher prices, the 0% promotional rate is a direct subsidy from the issuer to the cardholder — interest income the issuer forgoes in order to acquire a customer.

The subsidy is valuable when the cardholder uses it as a financing tool: planning a purchase, selecting the right card, setting up a fixed monthly payment that clears the balance before the deadline, and — for the financially disciplined — earning a return on the cash held aside during the promotional window. Under these conditions, 0% APR financing is a strict improvement over paying cash, producing $200 to $500 of free value on a typical large purchase.

The subsidy becomes a trap when the cardholder uses it as spending permission: financing purchases that would not have been made at the standard APR, paying only the minimum during the promotional period, losing track of the deadline, and arriving at the post-promotional cliff with a balance that will accrue interest at 20-29% for months or years. Under these conditions, the cardholder ends up paying more in post-promotional interest than the 0% period saved — and the issuer’s acquisition strategy has worked exactly as designed.

The math is clear. The discipline is the variable.

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Sources

• CARD Act of 2009 — Credit Card Accountability Responsibility and Disclosure Act, Pub. L. 111-24. Sections on grace period requirements, promotional rate disclosures, and payment allocation. congress.gov
• CFPB Consumer Credit Card Market Report — Ongoing biennial report covering promotional rates, deferred-interest financing, store card practices, and consumer outcomes. consumerfinance.gov
• CFPB — What is deferred interest? — Consumer advisory explaining how deferred-interest plans work and the risk of retroactive interest charges. consumerfinance.gov
• Federal Reserve — Consumer Credit G.19 Release — Monthly statistical release reporting outstanding revolving credit, average credit card interest rates, and consumer borrowing trends. federalreserve.gov
• FDIC — National Rates and Rate Caps — Savings account and money market account national rate data used for opportunity-cost calculations. fdic.gov
• Treasury Direct — Treasury Bill Rates — Auction results for 4-week, 13-week, and 26-week Treasury bills used for yield comparisons. treasurydirect.gov