Social Security COLA 2027: what the data says so far

The cost-of-living adjustment that will apply to Social Security benefits in 2027 is not a forecast, a proposal, or something officials will decide in the autumn. It is an arithmetic result, two-thirds of its inputs are already unknown only because the months have not happened yet, and the figure it will be measured against was locked in last September.

This page tracks that calculation as the data arrives. It is updated when the Bureau of Labor Statistics publishes each monthly CPI-W reading — the July figure in mid-August, August in mid-September, and September in mid-October, at which point the COLA is arithmetically determined and the Social Security Administration announces it within hours.

The formula, from the statute

The rule lives in 42 U.S.C. § 415(i). Three details in the actual text matter more than anything in the press coverage:

The index is CPI-W, not CPI-U. The Consumer Price Index for Urban Wage Earners and Clerical Workers covers a narrower population than the CPI-U that generates inflation headlines. The two diverge, sometimes meaningfully, because their spending baskets differ — CPI-W weights gasoline and transportation more heavily, which is why energy prices move the COLA more than they move the number you read about.

The measure is a quarterly average, not a single month. The statute specifies “the arithmetical mean of such index for the 3 months in such quarter”, and the relevant quarter is the one ending September 30. July, August and September carry exactly equal weight. A single hot or cold month moves the result by roughly a third of its own size.

The comparison is against the last year that produced a COLA. For 2027, that is the July–September 2025 quarter.

There is a fourth detail almost nobody explains, and it costs money: once the percentage is applied, benefit amounts that are “not a multiple of $0.10 shall be decreased to the next lower multiple of $0.10”. The rounding always goes down, never to the nearest cent.

The base figure is already fixed

The 2027 COLA will be measured against the CPI-W average for the third quarter of 2025:

Month	CPI-W
July 2025	316.349
August 2025	317.306
September 2025	318.139
Q3 2025 average	317.265

That number will not change. Every scenario below is the same division against the same denominator.

Where the 2026 data stands

CPI-W readings published so far this year, with June the latest available:

Month 2026	CPI-W	vs Q3 2025 base
January	317.942	+0.21%
February	319.422	+0.68%
March	323.500	+1.96%
April	326.541	+2.92%
May	328.829	+3.65%
June	327.075	+3.09%

Note what happened in June: the index fell, from 328.829 to 327.075. That single move knocked more than half a percentage point off where the running comparison stood in May.

This is the part of the COLA that almost no coverage connects. The June inflation report was received as good news — headline CPI dropped on the month, largely because energy prices fell nearly 5%. For a retiree whose benefit is indexed to CPI-W, that same drop is a smaller raise. Cooling inflation and a larger Social Security increase are, mechanically, opposites. You do not get both.

Scenarios, with three months still to measure

None of the July, August or September 2026 figures exist yet, so the following are not predictions. They are the arithmetic of three assumptions about what those months do, and they exist to show how much is still genuinely open:

If Q3 2026 averages…	Implied 2027 COLA
Flat at the June level (327.075)	3.1%
Rising ~0.2% per month	~3.5%
Falling ~0.3% per month	~2.5%

For reference, the COLA that took effect in January 2026 was 2.8%.

A useful way to hold this: on today’s data the 2027 adjustment is tracking modestly above the current one, but the range that remains genuinely reachable is roughly 2.5% to 3.5%, and energy prices are the single largest reason it might land at either end. Anyone publishing a confident single number in July is guessing at two-thirds of the inputs.

Checking the method

This calculation can be verified rather than trusted. Applying the same formula to last year — the Q3 2025 average of 317.265 against the Q3 2024 average of 308.729 — gives 2.7647%, which rounds to 2.8%. That is exactly the COLA that took effect in January 2026. The method reproduces the official result.

What actually reaches your bank account

The announced percentage is not what your deposit rises by, for three reasons worth separating.

The Medicare Part B premium is deducted first. For most beneficiaries the premium comes straight out of the Social Security payment, and it is announced separately by CMS in November — after the COLA. When the premium rises faster than the COLA in percentage terms, it absorbs part of the raise. In recent years it has absorbed a substantial share, and it is the main reason the increase people see is smaller than the one they read about.

The rounding goes down. As above, to the next lower ten cents, every time.

Taxes and withholding do not adjust automatically. A higher benefit can push more of it into the taxable range, because the thresholds that determine how much of a Social Security benefit is taxable are not indexed to inflation at all — $25,000 and $32,000, fixed in statute since 1984. A COLA can therefore raise your gross benefit and your tax bill at once. Our guide to the frozen Social Security tax thresholds and the tax torpedo runs the two-tier math under 26 U.S.C. §86, and the broader MAGI guide covers why each program measures income its own way.

The calendar from here

When	What lands	Why it matters
Mid-August 2026	July CPI-W	First of the three months; one-third of the answer
Mid-September 2026	August CPI-W	Two-thirds known; estimates narrow sharply
Mid-October 2026	September CPI-W	The COLA is determined; SSA announces the same day
November 2026	CMS announces the 2027 Part B premium	Determines what is left of the raise
January 2027	Increase appears in payments	Payment date depends on your birth date

The same October announcement carries the other figures for the year, including the amounts you can earn while collecting before full retirement age without benefits being withheld — the mechanics of that test, and the reason the withheld money is not actually lost, are in our guide to the Social Security earnings test.

Two companion pieces pick up where the announcement leaves off. The exact date the increase reaches your account — December 31, 2026 for some beneficiaries, a January Wednesday for most — is worked out in when the first 2027 COLA payment arrives. And because the Medicare Part B premium is deducted straight from the check, the raise that reaches your bank is smaller than the headline percentage; the net math after Part B runs those numbers, and the hold-harmless provision explains the statutory floor that keeps a premium jump from turning the raise negative.

The practical advice for anyone relying on this: no decision needs to be made before mid-October, and any figure circulating before then — including the ones on this page — is a scenario rather than a result. What is worth doing now is knowing which number to watch, and that number is the CPI-W, published in the middle of each month.

This page is updated with each CPI-W release through October.