Social Security’s annual cost-of-living adjustment isn’t voted on, negotiated, or set by any official’s judgment call. It’s a formula: the percentage change in a specific inflation index, measured over a specific three-month window, applied automatically to every benefit check the following January. Congress hasn’t had to pass a law to raise Social Security payments since 1975, and that’s by design.
The formula
The Social Security Administration compares the average CPI-W (the Consumer Price Index for Urban Wage Earners and Clerical Workers, a narrower cousin of the headline CPI-U used everywhere else on this site) for July, August, and September of the current year against the same three-month average from the last year a COLA was determined. If that average rose, benefits go up by the percentage increase, rounded to the nearest 0.1%, starting with checks paid in January. If it didn’t rise, benefits simply stay flat, there is no negative COLA, no matter how much CPI-W might have fallen.
COLA (%) = (Q3 average CPI-W, current year ÷ Q3 average CPI-W, last COLA year − 1) × 100
Two design choices matter here. Using a three-month average instead of a single month smooths out noisy monthly swings. And using CPI-W instead of CPI-U means the adjustment tracks a wage-earner spending basket, not the broader urban-consumer basket this site’s calculator uses; the two indexes usually move within a few tenths of a point of each other but occasionally diverge, most often over housing and medical care, where retirees’ and wage-earners’ spending patterns differ.
Why COLA has been zero, three times
Automatic annual COLAs began in 1975, following 1972 legislation that took the raise out of Congress’s hands and tied it to the CPI-W. Since then, the adjustment has come in at 0% three times: 2010, 2011, and 2016, years when the third-quarter CPI-W didn’t exceed its prior comparison point, largely because energy prices fell hard enough to pull the index down even as other categories rose. Retirees on a fixed income felt those flat years acutely, since a 0% COLA means a fixed benefit against whatever inflation, if any, was actually running.
Recent COLAs, and why the size varies so much
The COLA swings with whatever inflation happened to be doing the prior summer, which is why recent adjustments span such a wide range:
| Year | COLA |
|---|---|
| 2022 | 5.9% |
| 2023 | 8.7% |
| 2024 | 3.2% |
| 2025 | 2.5% |
Source: Social Security Administration, cost-of-living adjustments.
The 8.7% COLA that took effect in 2023 was the largest since 1981’s 11.2%, a direct consequence of the 2021 to 2023 inflation surge pushing CPI-W sharply higher through the summer of 2022. That’s the mechanism working as intended: a bigger price shock produces a bigger catch-up raise the following January, with a roughly six-month lag between the price increases actually happening and the benefit adjustment that offsets them.
What the lag means for retirees
Because the COLA is set once a year from a single three-month window, it’s always looking backward. A retiree’s benefit in January reflects the previous summer’s inflation, not the inflation happening right now, so in a year when prices are accelerating, real benefits lag behind the current cost of living for months before the next adjustment catches up; in a year when inflation is cooling, the opposite happens, and the COLA can briefly outrun the actual increase in prices. Over any run of several years, though, the formula does what it’s built to do: it keeps purchasing power roughly constant for the tens of millions of Americans whose income would otherwise be fixed against a cost of living that never stops moving.