Social Security COLA 2027: The Formula and the 317.265 Base
As of September 2026, nobody knows the 2027 Social Security COLA — including the Social Security Administration. That is not a hedge. The law ties the number to a three-month average, and one of those three months has not been published yet.
What you can know today is everything else: the exact formula, the base figure the 2027 adjustment will be measured against, and how much of the 2026 data is already on the books. This article walks through the SSA's own calculation, with the real CPI-W numbers it used for 2026, so you can do the arithmetic yourself the moment the last data point lands. It does not give you a forecast, and there is a section below explaining why the forecasts you have seen keep moving.
The formula, in the law's own words
The SSA states the rule plainly: a COLA effective for December of the current year equals the percentage increase, if any, in the CPI-W from the average for the third quarter of the current year to the average for the third quarter of the last year in which a COLA became effective. If there is an increase, it is rounded to the nearest tenth of one percent. If there is no increase, or the rounded increase is zero, there is no COLA for that year.
Three details in that sentence do most of the work. First, the index is CPI-W — the Consumer Price Index for Urban Wage Earners and Clerical Workers — not the headline CPI-U you see in news coverage. The Bureau of Labor Statistics calculates it monthly, and by law it is the official measure SSA must use.
Second, the comparison window is the third quarter only: July, August, and September. Inflation in January or May does not enter the calculation directly. It matters only insofar as it carries into the index level by July.
Third, the base is not simply last year. It is the third quarter of the last year in which a COLA became effective. In practice a COLA has become effective every year recently, so the base is the prior year's third quarter — but the wording exists because zero-COLA years happen. There were three of them this century: 2010, 2011, and 2016 all came in at 0.0 percent.
The 2026 COLA, worked out with real numbers
The 2026 adjustment is 2.8 percent. Here is how SSA got there, using its own published figures. The last year in which a COLA became effective was 2024, so the base is the average CPI-W for the third quarter of 2024.
| CPI-W | 2024 | 2025 |
|---|---|---|
| July | 308.501 | 316.349 |
| August | 308.640 | 317.306 |
| September | 309.046 | 318.139 |
| Third quarter total | 926.187 | 951.794 |
| Average | 308.729 | 317.265 |
Source: Social Security Administration, Latest Cost-of-Living Adjustment (retrieved September 2026). Averages rounded to the nearest 0.001.
The arithmetic SSA publishes is one line: (317.265 − 308.729) / 308.729 × 100 = 2.8 percent. That 2.8 percent applies to Social Security benefits beginning with the December 2025 benefit, which is payable in January 2026. Federal SSI payment levels rose 2.8 percent effective for January 2026 payments — but because the normal SSI payment date is the first of the month and January 1 is a holiday, January SSI payments are always made at the end of the previous December.
What that makes the 2027 base: 317.265
Read the formula once more and the next base falls out of it. A COLA became effective in 2025, so the adjustment effective for December 2026 — the one that shows up in January 2027 payments — is measured against the average CPI-W for the third quarter of 2025, which is 317.265.
So the calculation waiting to be completed is:
Take CPI-W for July 2026, August 2026 and September 2026. Add them. Divide by three. Call that Q3-2026.
Then: (Q3-2026 − 317.265) / 317.265 × 100, rounded to the nearest tenth of one percent.
If the rounded result is zero or negative, there is no COLA.
That is the whole thing. No model, no forecast, no proprietary methodology. Once BLS publishes the September 2026 figure, anyone with a calculator gets the same answer SSA does.
The 2026 CPI-W data published so far
Here is what SSA's CPI-W table shows for 2026 as of September 2026. Seven months are on the books, January through July.
| Month (2026) | CPI-W |
|---|---|
| January | 317.942 |
| February | 319.422 |
| March | 323.500 |
| April | 326.541 |
| May | 328.829 |
| June | 327.075 |
| July | 327.104 |
| August | not yet published |
| September | not yet published |
Source: Social Security Administration, CPI-W table (retrieved September 2026)
One of the three quarter-three months is in. For reference, July 2026 at 327.104 sits 3.1 percent above the 317.265 base. Be careful with that number: it is one month measured against a three-month average, not a COLA. It tells you the direction, not the answer. August and September can pull the quarterly average either way, and in 2026 the monthly series has not moved in one direction — it rose through May, then fell in June and was roughly flat in July.
Two rules that break naive estimates
Forecasts you see in the press are usually built by assuming the remaining months follow a trend. Two features of the statute make that shakier than it looks.
Rounding to the nearest tenth. The final figure is rounded to one decimal place. A quarterly average that lands at 2.749 percent becomes 2.7 percent; 2.751 becomes 2.8 percent. Two forecasts that differ by a rounding error in the third month can print different headline numbers, which is part of why estimates published weeks apart disagree.
No increase means no COLA. The law has no provision for a negative adjustment. If the Q3 average comes in below the base, benefits do not fall — the COLA is simply zero. That has happened three times since 2009: 0.0 percent for 2010, 2011 and 2016. Any estimate implying a benefit cut is misreading the statute.
It is also worth knowing how wide the historical range is, because it explains why a single month's inflation print does not settle much. Recent adjustments: 8.7 percent for 2023, 3.2 percent for 2024, 2.5 percent for 2025, 2.8 percent for 2026. Further back the series runs from 0.0 percent up to 14.3 percent in July 1980.
The month BLS never published
This detail belongs in any discussion of COLA timing, and it is rarely mentioned. SSA's own CPI-W table carries a footnote for October 2025: BLS did not publish an October 2025 Consumer Price Index. The stated reason is a lapse in appropriations — BLS could not collect the October 2025 reference period survey data and was unable to collect it retroactively.
October is not one of the three months the COLA uses, so the 2026 adjustment was unaffected. But it is a concrete reminder that the input to this formula is a government statistical program, not a market feed. The calculation cannot run ahead of the data, and the data has recently failed to appear at least once.
When you see it, and what moves with it
For the 2026 cycle, SSA made COLA notices available online in the Message Center of the my Social Security account in late November 2025, with the increase appearing in January 2026 payments. If the 2027 cycle follows the same pattern, the notice arrives in the account before the payment changes — and SSA points out you can choose to receive notices online instead of by mail.
The COLA is not the only figure that resets. For 2026, SSA published these alongside it:
| 2026 figure | Amount |
|---|---|
| Maximum earnings subject to Social Security tax | $184,500 |
| Earnings limit, below full retirement age ($1 withheld per $2 over) | $24,480 |
| Earnings limit, year you reach FRA ($1 per $3 over, until FRA month) | $65,160 |
| Earnings limit at or above FRA all year | no limit |
Source: Social Security Administration, COLA Information for 2026 (retrieved September 2026)
These are 2026 amounts. This article does not list 2027 figures, because SSA has not published them. They are set through the same annual process and appear with the COLA announcement.
- Write down the base: 317.265
- Collect CPI-W for July, August and September 2026 (July is already 327.104)
- Average the three, subtract 317.265, divide by 317.265, multiply by 100
- Round to one decimal. Zero or negative means no COLA
FAQ
What is the 2027 Social Security COLA?
It has not been determined. The figure depends on the average CPI-W for July, August and September 2026, and as of September 2026 only the July value is published. Any number circulating now is an estimate, not the COLA.
What number will the 2027 COLA be measured against?
The average CPI-W for the third quarter of 2025, which is 317.265. A COLA became effective in 2025, so under the statutory formula that quarter becomes the base for the adjustment effective December 2026.
Which inflation index does Social Security use?
CPI-W, the Consumer Price Index for Urban Wage Earners and Clerical Workers, calculated monthly by the Bureau of Labor Statistics. By law it is the official measure SSA uses for COLAs. It is not the same as the headline CPI-U reported in most news coverage.
Can benefits go down if inflation falls?
No. The statute provides for an increase or no change. If there is no increase, or the rounded increase is zero, there is no COLA for that year. It happened three times recently: 0.0 percent for 2010, 2011 and 2016.
What was the 2026 COLA and when did it take effect?
2.8 percent. It applies beginning with the December 2025 Social Security benefit, which is payable in January 2026. Federal SSI payment levels rose 2.8 percent effective for January 2026 payments, paid at the end of December 2025 because January 1 is a holiday.
Why do published 2027 estimates keep changing?
Because they are built on assumptions about months that have not been measured, and because the final figure is rounded to the nearest tenth of one percent. A small difference in the September reading can move the rounded headline number.
The bottom line
The 2027 COLA is not a forecast problem for you to solve — it is one subtraction waiting on one data release. The base is 317.265. July 2026 came in at 327.104. Two months remain, and when the September figure publishes, the answer is arithmetic.
If you are planning around it, plan around the mechanism rather than a headline: the increase applies to the December benefit paid in January, the notice appears in your my Social Security Message Center before the payment changes, and the tax and earnings figures reset in the same announcement. That is the part you can act on today.
This article is for general information only and is not financial, tax, or legal advice. Every figure above is taken from the Social Security Administration pages linked below, retrieved September 2026. It deliberately contains no estimate or projection of the 2027 COLA, and no 2027 tax or earnings figures, because SSA has not published them. Rules change — verify with the official sources linked above or consult a licensed professional before acting.
Social Security Administration · Cost-of-Living Adjustment (COLA) Information
Social Security Administration · Latest Cost-of-Living Adjustment (formula and computation)
Social Security Administration · CPI-W monthly table