Tax season prep — the year-round runway to file confidently

The IRS opens individual tax filing season in mid-to-late January each year and the federal filing deadline is April 15 (or the next business day). Most US households treat tax season as a 6-8 week sprint between when they receive their final W-2 / 1099 / 1098 documents (early February) and the April deadline. The structural problem with this approach: many tax-planning decisions that produce meaningful savings have to be made BEFORE December 31 of the tax year. By the time filing season starts in January, the planning window for the tax year just ended is mostly closed.

Spreading the work across the spring-through-fall months of the tax year is enough to organize documents, verify withholding adequacy, execute year-end planning moves, and arrive at filing season with the return already substantially built. This piece walks through the month-by-month checklist for households who want to file confidently and capture every available optimization, including the specific timing of decisions that must happen before year-end. Wherever you are in the calendar, pick up at the current month and work the cadence forward; the checklist is an annual loop, not a one-time countdown.

Month-by-month checklist

May:

• Pull your prior-year tax return and confirm the AGI line — you’ll need it as identity verification for e-filing the upcoming year.
• Verify your W-4 withholding is accurate for current-year income via IRS Tax Withholding Estimator (irs.gov/individuals/tax-withholding-estimator). Major life events (marriage, divorce, new child, new job) since the last W-4 should trigger a fresh submission.
• If self-employed, verify your year-to-date 1040-ES quarterly estimated payments are on track for safe-harbor (100% of last year’s tax, or 110% if AGI exceeded $150K).
• Confirm your tax-advantaged account contributions are on track for the year: HSA on schedule, Roth IRA progressing, 401(k) elective deferral pace appropriate.

June:

• Mid-year W-4 check using the IRS Estimator with updated income picture.
• Review prior-year tax return for any deductions/credits missed (Form 1040-X amendments are still possible up to 3 years post-filing).
• If you have substantial RSU vesting, check your year-to-date supplemental withholding adequacy.
• For households on ACA marketplace insurance, mid-year income re-estimate — if income is meaningfully higher or lower than initial MAGI estimate, update the marketplace to avoid Premium Tax Credit reconciliation surprise.

July:

• Begin organizing the year-end document folder. Pull January-June statements for your taxable brokerage accounts, mortgage interest paid, property tax paid YTD.
• If you have charitable giving plans, schedule them with calendar-aware timing — donor-advised fund contributions before year-end may bunch deductions efficiently.

August:

• Calendar critical dates: third estimated tax payment due September 15 if applicable.
• Review traditional IRA contribution status — if income approaches Roth phase-out, plan for backdoor Roth execution before year-end.

September:

• Third quarter estimated tax payment due September 15.
• Begin year-end tax-loss harvesting evaluation if you have a taxable brokerage account with positions that have lost value. See our tax-loss harvesting guide for mechanics.
• Review your 401(k) elective deferral pace. If you intend to max for the year, calculate the per-paycheck deferral needed for the remaining pay periods.

October:

• Tax-loss harvesting execution window if applicable. Wash sale rule requires 31-day wait, so harvests in October still produce realized losses for the current tax year if completed by year-end.
• For households age 73+, verify required minimum distributions (RMDs) are on track for the year.
• IRS publishes annual inflation adjustments late October / early November — note next year’s limits for next-year planning.
• For S-corp election candidates, Form 2553 election for the FOLLOWING tax year is due by March 15 of the following year — start the documentation now.

November:

• IRS announces next year’s contribution limits and tax bracket adjustments. Plan your next-year 401(k) elective deferral target.
• Roth conversion timing: if executing a Roth conversion to fill the 12% or 24% bracket, finalize the conversion amount and execute before December 31.
• Charitable giving: any donor-advised fund contributions or direct charitable gifts for the current tax year must be completed by December 31.
• HSA contributions: have until the tax-filing deadline to contribute, but November is a good time to verify you’re on track.

December:

• Final tax-loss harvesting executions before December 31.
• Roth conversion executions before December 31.
• Charitable giving completions before December 31.
• Final 401(k) elective deferral contributions (deducted from December paychecks).
• HSA contribution catchup if behind.
• Required minimum distributions for age 73+ households must be completed by December 31 (first RMD year has an April 1 grace exception).

Decisions that MUST happen before December 31

These are the moves that have a hard year-end deadline. If you miss them, the opportunity is gone for that tax year:

1. Tax-loss harvesting — losses must be realized (security sold) by December 31 to apply against current-year gains
2. Roth conversion — converted amount counts as current-year ordinary income only if conversion completed by December 31
3. Required minimum distribution (age 73+) — must be withdrawn by December 31 (or April 1 of following year for first RMD year)
4. Charitable giving (cash or appreciated stock) — must be transferred by December 31 to claim current-year deduction
5. 401(k) elective deferral — withholding from December paychecks is the last chance to contribute (subject to plan’s specific payroll deadlines)
6. Final HSA contribution — has until tax-filing deadline (typically April 15) to contribute for prior year, BUT some employers cut off payroll HSA contributions on December 31
7. Required Minimum Distribution conversion to qualified charitable distribution (age 70½+) — QCD must complete by December 31 to count for the year

Decisions that have January-April flexibility

These have until tax-filing deadline (typically April 15 of the following year):

1. Traditional IRA contributions for prior tax year
2. Roth IRA contributions for prior tax year
3. HSA contributions for prior tax year (if not blocked by employer payroll cutoff)
4. SEP-IRA contributions for self-employed (extends until tax-filing deadline + any extension)
5. Tax filing itself (can request 6-month extension via Form 4868)

The January-April flexibility means a household who has cash flow to fund these but hasn’t yet has time after year-end. Use the time to verify the contribution makes sense given the actual final tax picture.

What to verify each year

• IRS Get Ready page: irs.gov/individuals/get-ready-to-file-your-tax-return
• IRS Free File availability for your AGI level: irs.gov/filing/free-tax-prep-options
• Do not plan around IRS Direct File: the IRS-operated free filing pilot was discontinued and is not available for the 2026 filing season. Free File guided software (AGI $89,000 or less) and Free File Fillable Forms are the remaining free federal routes.
• Tax bracket and standard deduction for the year you’re filing: irs.gov/forms-pubs/about-publication-501
• Contribution limits at irs.gov/retirement-plans/cola-increases-for-dollar-limitations-on-benefits-and-contributions

What this guide does not cover

This piece focused on the calendar-year prep for individual federal income tax filing. It does not cover:

• State tax filing prep which has its own calendar and forms (typically due same date as federal)
• Business tax filing for entities (different deadlines, Form 1120/1120-S/1065)
• Trust and estate tax planning
• Audit response preparation
• Tax debt resolution for households with prior-year unpaid balances

For the mainline US individual income tax filing preparation, the framework above is complete.

A year-round runway converts tax filing from a stressful sprint into a structured workflow. Households who follow the month-by-month checklist arrive at January with documents organized, withholding correct, and year-end moves executed — meaning the actual filing in February-April is just data entry, not crisis management. The optimization gains from prep are typically several hundred to several thousand dollars per household per year.