Each October, the Social Security Administration announces the one number nearly every retiree in the country is waiting for: the cost of living adjustment, or COLA. That number decides how much monthly benefits go up in January. The math fits on an index card, and it uses a price index most people have never heard of.
The index behind the number
The COLA isn't based on the headline CPI you hear about most often. The Social Security Administration uses the Consumer Price Index for Urban Wage Earners and Clerical Workers, called CPI-W for short. The Bureau of Labor Statistics publishes it every month, right alongside the better-known CPI-U.
CPI-W covers households that get more than half their income from clerical or wage occupations. That's a narrower group than CPI-U, which covers all urban consumers.
The three-month comparison
Here's how SSA describes the calculation:
- Take the average CPI-W for July, August, and September of the current year.
- Take that same three-month average from the last year a COLA was determined.
- The percentage increase from one to the other, rounded to the nearest tenth of a percent, is the COLA.
No increase means no COLA. Benefits don't go down when prices fall.
September's CPI-W comes out in October, which is why the announcement lands in October. The increase first shows up in benefits payable in January.
A worked example with made-up numbers
Say the third-quarter average CPI-W was 300.0 last year and 309.0 this year.
(309.0 − 300.0) ÷ 300.0 = 0.03, or 3.0 percent.
Someone getting $1,800 a month would see that go up by 3.0 percent, to $1,854, before any changes to Medicare premiums or tax withholding. These numbers are only an illustration, not figures from any actual year.
Why your raise can feel smaller than the COLA
Three things often shrink the check that arrives.
Medicare Part B premiums. For many beneficiaries, the Part B premium comes straight out of the Social Security payment. When that premium goes up in the same January, part of the COLA goes toward covering it.
Taxes. Depending on your combined income, part of your Social Security benefit can be subject to federal income tax. The IRS lays out the thresholds in Publication 915.
Your basket isn't CPI-W. CPI-W reflects how working households spend. Older adults often put a bigger share of their money toward health care and housing. To study that difference, BLS has published an experimental index for Americans 62 and older, called R-CPI-E. It's research data, and it isn't used to set benefits.
The COLA also moves other numbers
The same adjustment carries into other parts of the program. SSA raises Supplemental Security Income payment levels by the COLA, and each fall it announces related figures too, like the maximum earnings subject to the Social Security tax and the earnings test limits for people who claim before full retirement age. Those other figures run on their own formulas, so check SSA's annual fact sheet for each one.
A short history of automatic COLAs
Benefit increases weren't always automatic. Before the mid 1970s, Congress had to pass a new law every time it wanted to raise benefits. SSA's actuarial office lists automatic cost of living adjustments beginning in 1975, and the CPI-W third quarter method described above is the current form of that rule.
Recent years show how much the number can swing:
- 2023: SSA announced an 8.7 percent increase in October 2022, after the inflation surge of 2021 and 2022. It was the largest adjustment in decades.
- 2026: SSA announced a 2.8 percent increase in October 2025.
- 2027: SSA's COLA page lists a 3.6 percent increase, starting with benefits payable in January 2027. Higher SSI payments begin December 31, 2026.
Big COLAs feel generous, but they show up after prices have already gone up. A beneficiary who saw grocery and rent bills climb through 2022 had to wait until January 2023 for the adjustment that reflected it. That lag is built right into the formula, since it looks back at July through September.
Why not use CPI-U or a senior index?
This question comes up every time a COLA is announced. CPI-W covers a smaller slice of the population than CPI-U, and neither is designed around the spending of retirees. BLS's experimental R-CPI-E reweights the index toward the spending patterns of households 62 and older, which tend to put more toward housing and medical care. BLS itself labels it a research series with limitations: it uses the same prices as the regular index rather than prices collected from the stores and services older people actually use, and its sample is smaller. Switching the COLA to any other index would take an act of Congress.
What the COLA does not change
The COLA raises the benefit you already have. It doesn't change your earnings record, your full retirement age or the reduction for claiming early. If you haven't claimed yet, your future benefit is still adjusted for COLAs from age 62 onward, so you don't lose the adjustments by waiting.
Reading your notice
SSA mails a COLA notice in December showing your new benefit amount, any Medicare premium deduction and the net payment. If you have a my Social Security account, SSA says most beneficiaries can read the notice in the Message Center starting in late November, weeks before the letter arrives. Put the gross increase next to the net change. That's the fastest way to see how much of your raise went to Medicare Part B.
Estimating next year's COLA yourself
The formula is public, so you can follow along as the year goes on. BLS releases CPI-W each month alongside CPI-U, usually in the middle of the following month. When the July figure comes out in August, you have one of the three months that will count. Add August and September as they are released, average the three, and compare with the same average from the prior year. The result will match SSA's announcement once the September data is in, because SSA uses exactly those published index values. Until then, any forecast you see is just an estimate built on guesses about the months still to come.
How to use this on our calculator
The COLA answers one narrow question: did average prices for wage-earning households go up between two late-summer periods? To ask your own question, like "what does my $1,800 from five years ago buy today?", use our calculator with the CPI series and the time period you care about. Then put that result next to the COLAs you actually received over those same years. If the calculator number is bigger, your benefit fell behind.
Sources
- Social Security Administration, "Cost-of-Living Adjustment (COLA) Information": https://www.ssa.gov/cola/
- Social Security Administration, "Latest Cost-of-Living Adjustment" and COLA computation: https://www.ssa.gov/oact/cola/latestCOLA.html
- U.S. Bureau of Labor Statistics, CPI-W and CPI-U: https://www.bls.gov/cpi/
- BLS, research index for older Americans (R-CPI-E): https://www.bls.gov/cpi/research-series/r-cpi-e-home.htm
- IRS, Publication 915, Social Security and Equivalent Railroad Retirement Benefits: https://www.irs.gov/publications/p915
- Social Security Administration, "Automatic Determinations" (COLA history): https://www.ssa.gov/oact/cola/autoAdj.html
- Social Security Administration, "Social Security Announces 8.7 Percent Benefit Increase for 2023" (October 13, 2022): https://www.ssa.gov/news/en/press/releases/2022-10-13.html
- Social Security Administration, "Social Security Announces 2.8 Percent Benefit Increase for 2026" (October 24, 2025): https://www.ssa.gov/news/en/press/releases/2025-10-24.html