How we computed these
Federal tax parameters are not set by anyone's judgment. The tax code indexes them to chained CPI-U, averaged over the 12 months ending August 31 of the preceding year. August 2026 data published on September 11, which made every input to the formula known.
The code applies that average to the statutory base amounts and rounds the resulting increase the way the law directs — which is not the same as rounding the final number, and is the detail most informal projections get wrong. Before producing any projection it checks itself against the published 2026 figures, and currently reproduces all 27 of them exactly. If that check ever fails, the projection does not print.
The one month that is missing
Chained CPI-U for October 2025 does not exist. The federal shutdown stopped data collection, and rather than estimate the month, the Bureau of Labor Statistics cancelled the release — the first break in a series that had run continuously since 1921. That month falls inside the 12-month window these figures index on.
We average the 11 months that were published, which is the reading closest to what the statute actually says. The alternative, interpolating a value for October from the months either side, produces thresholds roughly $25 to $150 lower. The IRS has not said which approach it will take, and this is the single largest source of uncertainty in any 2027 projection published right now — including ours. It is also why projections on different sites do not match each other.
If our figures turn out to differ from the official ones, this is almost certainly why, and the difference will be logged on our methodology page.
What isn't known yet for 2027
Several widely-searched 2027 figures genuinely cannot be computed today, and we would rather say so than publish an estimate dressed up as a calculation:
- Social Security wage base. Indexes to the national average wage index, which tracks earnings rather than prices, so inflation data cannot produce it. The Social Security Administration announces it in mid-October.
- 401(k), IRA, and other retirement limits. A separate IRS release, usually in early-to-mid November, with its own rounding rules.
- Standard mileage rate. Announced in December, and based on a cost study rather than on inflation.
- State income tax brackets. Most states index on their own schedules and publish between November and January. A handful have already enacted 2027 rate changes in statute, but thresholds and deductions are not yet set.
When these become official
The IRS Revenue Procedure with official 2027 figures is expected in October 2026. We replace these projections with the official numbers the day it publishes, and remove the projection labels in the same change. Until then, everything on this page is a calculation, clearly marked as one.
For figures you can rely on today, the 2026 tax reference covers confirmed brackets, deductions, retirement limits, and the Social Security wage base. Our tax calculators all run on 2026 data.
Frequently asked questions
Are these the official 2027 tax brackets?
No. These are projections. The IRS publishes official 2027 figures in a Revenue Procedure expected in October 2026. We compute these from the same inflation data and the same formula the IRS is required to use, which is why projections published a month early are usually accurate — but they are not official, and we replace them the day the IRS figures land.
How can 2027 brackets be calculated before the IRS announces them?
Federal tax parameters are not set by discretion. The tax code indexes them to chained CPI-U averaged over the 12 months ending August 31 of the prior year. Once August data publishes — September 11, 2026 in this case — every input to the formula is known, so the figures are computable rather than guesswork. The IRS announcement confirms a calculation anyone can run.
Why do different websites show slightly different 2027 projections?
Mostly because of one missing month. Chained CPI-U for October 2025 was never collected — the federal shutdown stopped data collection and the Bureau of Labor Statistics cancelled the release rather than estimating it. That month falls inside the 12-month window the 2027 figures index on, and there is no published guidance on how to handle the gap. Averaging the 11 months that exist, interpolating a value for the missing one, and other approaches each produce slightly different brackets. We average the 11 published months, which is the reading closest to the statutory text.
Why is the 2027 Social Security wage base not listed here?
Because it cannot be computed from inflation. The wage base indexes to the Social Security Administration national average wage index, which tracks earnings rather than prices, and it is announced separately in mid-October. Any site publishing a 2027 wage base right now is estimating it, not calculating it.
What about 2027 401(k), IRA, and HSA limits?
Those come from separate IRS releases later in the year — retirement limits in November, and the mileage rate in December. They use different rounding rules and different base amounts from the bracket tables, so they are not derivable from the data behind this page. We add them as each release lands.
How much are the 2027 brackets going up?
The inflation adjustment works out to about 3.19%. Every bracket threshold and the standard deduction rise by roughly that amount, which means that if your income rose by less than that, slightly more of it falls in lower brackets than it did in 2026.