2027 capital gains brackets: the 0% band clears $100,000

The math behind the 2027 capital gains brackets closed on September 11, 2026, the day the Bureau of Labor Statistics published the August chained CPI-U reading — the last of the twelve months that decide these numbers under federal statute. The short answer: the joint 0% long-term capital gains threshold is projected at $102,100 (or $101,950 under an alternate treatment of one missing data month), the first time that figure has ever cleared six figures for a married couple filing jointly.

The statute and the rounding

Long-term capital gains and qualified dividends are taxed on a three-step federal ladder — 0%, 15%, and 20% — and the two breakpoints between those steps are not tied to the ordinary income tax brackets the way many filers assume. Since 2018, 26 U.S.C. § 1(j)(5) fixes them as their own dollar amounts, the “maximum zero rate amount” and the “maximum 15-percent rate amount,” each indexed for inflation independently and rounded down to the nearest multiple of $50. Two of the figures are not indexed on their own at all. The statute defines the 0% ceiling for single and married-filing-separately filers as one half of the joint amount in effect for the year, and the married-filing-separately 15% ceiling as half the joint 15% figure. Halving a multiple of $50 can land on $25, which is why the single 0% line can end in 75 when the joint line does not.

Both breakpoints are measured against taxable income — the figure on Form 1040 after the standard or itemized deduction — not against wages, AGI, or modified AGI. Long-term gains stack on top of ordinary income for this purpose: the ordinary income fills the bottom of the ladder first, and only the portion of the gain that still fits under a given ceiling is taxed at that step’s rate.

The indexing formula itself borrows the same machinery that sets the ordinary tax brackets and the standard deduction, laid out in § 1(f)(3): a twelve-month average of the Chained Consumer Price Index for All Urban Consumers, running from September of one year through August of the next. The 2017 statutory base amounts being adjusted are $77,200 (joint) for the 0% ceiling, and $479,000 (joint) and $425,800 (single) for the 15% ceiling; head of household starts from $51,700 and $452,400. The single 0% ceiling then follows as half the adjusted joint figure. Those base figures, run through the chained-CPI ratio for the applicable window and rounded down to the nearest $50, are what produce every number in the table above.

Checking the method against 2026

A formula that cannot reproduce a year the IRS has already published is not worth trusting for a year it has not. Rev. Proc. 2025-32, released October 9, 2025, set the confirmed 2026 figures: $98,900 and $613,700 for married filing jointly, $49,450 and $306,850 for married filing separately, $66,200 and $579,600 for head of household, and $49,450 and $545,500 for single filers. Running the same 2017 base amounts through the chained-CPI window that closed in August 2025 reproduces all six of those thresholds exactly. That is the same method applied below to the window that closed in August 2026, and it is the reason this projection is arithmetic rather than a guess: a single ratio, applied to six statutory base amounts, lands on every published 2026 figure without adjustment, and in the broader indexing check across this site’s inflation-tracking work, a single window average has reproduced eighteen of eighteen tested 2026 figures from the same revenue procedure.

The October 2025 question

Every 2027 figure in the table above carries a caveat, because one of the twelve months in the averaging window does not exist. The Bureau of Labor Statistics never published a chained CPI-U reading for October 2025; data collection was disrupted by that year’s government shutdown, and the gap was never filled in afterward. The window that decides the 2027 brackets — September 2025 through August 2026 — has eleven real months and one hole.

The IRS has two ways to handle that. It can average the eleven months that do exist and use that average for the full year, or it can substitute an estimate for the missing October reading and average all twelve. The two approaches produce slightly different results, shown as the unrounded figures behind the table: for the joint 0% ceiling, $102,118.40 under the eleven-month approach against $101,991.60 with an October estimate folded in — both of which round down to $102,100 and $101,950 respectively. The other ceilings show the same pattern, with gaps as small as $50 (head of household’s 0% line) and as large as $800 (the joint 15% line). The single 0% line is the one oddity: because it is half the joint figure, the imputed reading gives $50,975, a number that ends in 75 even though every indexed amount is rounded to $50. Under either treatment, the qualitative headline is unchanged: the joint 0% band clears $100,000 for the first time.

Neither the IRS nor the Bureau of Labor Statistics has said in public which treatment it will use. The 2027 brackets and standard deduction will arrive first, in a revenue procedure this site’s IRS 2027 inflation adjustments tracker is watching for, expected sometime between mid-October and November 2026 based on the October 9, 2025 precedent Rev. Proc. 2025-32 set for 2026.

What it means for gain harvesting

A wider 0% ceiling means more room to realize long-term gains at zero federal tax before a household’s taxable income spills into the 15% bracket — the mechanic behind tax-gain harvesting. Comparing the same household’s position in 2026 and in 2027 shows how much that room actually grows.

Take a married couple filing jointly with $93,200 of ordinary income (wages, pension, and interest) and no other deductions, in both years. In 2026, subtracting the $32,200 joint standard deduction leaves taxable income of $61,000, and the 0% ceiling of $98,900 leaves $37,900 of room to realize long-term gains at zero tax. In 2027, the same $93,200 of nominal income against the $33,200 standard deduction projected for that year leaves taxable income of $60,000, and the projected $102,100 ceiling leaves $42,100 of 0% room — or $41,950 under the October-imputed treatment.

That is $4,200 of extra harvesting room year over year ($4,050 under the alternate treatment), and at the 15% rate that room would otherwise be taxed at, it is $630 of federal tax the household avoids simply by harvesting up to the higher ceiling ($607.50 under the alternate treatment). Of that $4,200, $3,200 comes from the higher 0% ceiling and $1,000 from the larger standard deduction, which lowers the household’s taxable ordinary income before the gains are stacked on top.

One caveat belongs in every harvesting discussion regardless of the year: realizing a gain, even one taxed at 0% federally, still raises adjusted gross income. That can matter for programs that key off AGI rather than taxable income — an Affordable Care Act marketplace premium tax credit calculated for the same year, or Medicare IRMAA surcharges calculated from AGI two years later. Neither of those effects has a dollar figure attached here; they are simply a reason to look at the full picture before harvesting a large gain, not just the federal capital-gains line.

What doesn’t move: the NIIT

Not every number tied to capital gains rides the same inflation escalator. The 3.8% Net Investment Income Tax, under 26 U.S.C. § 1411, applies to net investment income above a modified AGI threshold of $250,000 for married filing jointly or $200,000 for single filers — and both figures are fixed in the statute itself, with no inflation-adjustment mechanism at all. They will be the same in 2027 as they were the year the tax took effect, and the same as they were in 2026.

That asymmetry means the gap between the rising 0% bracket ceiling and the flat NIIT threshold widens every year, not that the two interact directly — a household harvesting gains inside the 0% bracket is nowhere near the NIIT threshold in the first place. The asymmetry matters more for higher earners, where a capital-gains bracket that keeps climbing does nothing to move a NIIT threshold that has stayed put since enactment. Two other capital-gains rates sit entirely outside this indexing question as well: the 28% maximum rate on collectibles gains, covered in the 28% Rate Gain Worksheet walkthrough, and the 25% rate on unrecaptured Section 1250 gain from real estate depreciation. Both have their own fixed maximum rates, untouched by the CPI math discussed here.

The calendar from here

The 2027 figures in this piece are a projection, not a confirmation, and they stay that way until the IRS acts. The precedent for timing is Rev. Proc. 2025-32, which set the 2026 figures on October 9, 2025; the 2027 revenue procedure is expected in the same mid-October-to-November window, though no specific date has been announced as of this writing. Whichever way the IRS resolves the October 2025 gap will settle every figure in this piece at once, since all six thresholds move together off the same chained-CPI window. For the 0% and 15% capital gains ceilings, watch the inflation adjustments tracker, which follows the same revenue procedure and the same open question across the rest of the 2027 tax figures — including the 2027 Roth IRA and IRA deduction phase-outs, indexed under the identical August-ending window. For the underlying mechanics of how these brackets interact with ordinary income, see capital gains tax explained.

Sources

• 26 U.S.C. § 1 — law.cornell.edu/uscode/text/26/1, for § 1(h) rate structure, § 1(j)(5) capital gains breakpoints, and § 1(f)(3) cost-of-living formula
• 26 U.S.C. § 1411 — law.cornell.edu/uscode/text/26/1411, Net Investment Income Tax
• IRS Rev. Proc. 2025-32 — irs.gov/pub/irs-drop/rp-25-32.pdf, confirmed 2026 capital gains thresholds
• Bureau of Labor Statistics, Chained CPI-U series SUUR0000SA0 — August 2026 reading published September 11, 2026
• finbarrow, IRS 2027 inflation adjustments tracker — companion page for the shared CPI window and the October 2025 imputation question