How the Social Security COLA Is Calculated
The Social Security cost-of-living adjustment (COLA) for 2027 will be set by one measure, the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W), compared over one window: the average for July, August and September 2026 against the average for the same three months of 2025. The percentage increase, rounded to one decimal place, becomes the COLA for benefits payable from January 2027. If the index does not rise, there is no COLA, and benefits are not cut. Because the inputs are public, you can follow the calculation yourself from Bureau of Labor Statistics (BLS) data before the official announcement, which normally comes in October after the September index is published.
Step 1: Use the Right Index
News headlines usually report the CPI-U, the index for all urban consumers. The COLA uses the CPI-W, which reflects the spending of households that earn most of their income from wages and clerical work. The two often move similarly but can differ by a few tenths of a percentage point. On the BLS website, the CPI-W for the U.S. city average, all items, not seasonally adjusted, is series CWUR0000SA0. That is the series to use.
Step 2: Collect the Third-Quarter Values
Here are the published BLS values for that series, retrieved from the BLS public data API on October 9, 2026:
| Month | 2024 | 2025 | 2026 |
|---|---|---|---|
| July | 308.501 | 316.349 | 327.104 |
| August | 308.640 | 317.306 | 328.481 |
| September | 309.046 | 318.139 | Not yet published on October 9, 2026 |
| Third-quarter average | 308.729 | 317.265 | Pending |
Source: U.S. Bureau of Labor Statistics, CPI-W, series CWUR0000SA0 (index base 1982–84 = 100). Averages are our arithmetic from the published monthly values.
Step 3: Apply the Formula
COLA = (average of July–September this year ÷ average of July–September last year − 1) × 100, rounded to the nearest tenth of a percent.
Checking the formula against a known result: the 2025 third-quarter average of 317.265 divided by the 2024 average of 308.729 gives an increase of 2.8%, which is the COLA that applied to benefits from January 2026. That confirms the series and the method.
For 2027, only two of the three months were available when this page was updated. Comparing the July–August 2026 average (327.793) with the July–August 2025 average (316.827) gives an increase of about 3.5%. That is an interim figure, not the 2027 COLA. The September value can move the final number, and only the Social Security Administration's announcement is official.
Setting it up in a spreadsheet
Put the three months of last year in cells B2 to B4 and the months of this year in C2 to C4 as they are published. In B5 enter =AVERAGE(B2:B4) and in C5 =AVERAGE(C2:C4). The COLA estimate is =ROUND((C5/B5-1)*100,1). While only some months of the current year are out, compare the same months of both years, not a partial average against a full one, or the estimate will be biased. When the September value appears, replace the interim result with the full-quarter calculation, and keep the sheet: next year you only need to add a new column. The same sheet can hold your current benefit and Part B premium, so the net change is calculated in one place.
Step 4: Turn the Percentage Into Your Benefit
Multiply your current monthly benefit before deductions by the COLA percentage to estimate the gross increase. For a hypothetical $2,000 benefit, each 1% of COLA adds about $20 a month. The actual figure in your notice can differ slightly because of rounding rules. Your Social Security statement and the COLA notice in your my Social Security account show your own numbers.
Then subtract what comes out of the check
Many beneficiaries have Medicare Part B premiums deducted from their benefit. The Part B premium for the coming year is announced separately by the Centers for Medicare & Medicaid Services, usually in the autumn. If the premium rises, part of the COLA goes to the higher premium. Higher-income beneficiaries may also pay an income-related surcharge (IRMAA), which is based on tax returns from two years earlier. Your "net COLA" is the gross increase minus any increase in these deductions and any change in tax withholding.
Step 5: Check the Tax Side
Part of your Social Security benefit can be taxable when your combined income passes thresholds set in the tax code; the IRS explains the calculation in Publication 915. A higher benefit can therefore change how much of it is taxed, and it can change your withholding needs. If you have federal tax withheld from benefits, review the withholding choice each January.
Where to Follow the Data
| What | Where | When |
|---|---|---|
| Monthly CPI-W values | BLS CPI release and data tools (series CWUR0000SA0) | Monthly, about mid-month for the prior month |
| Official COLA | Social Security Administration announcement | Usually October, after the September CPI is published |
| Your new benefit amount | COLA notice in your my Social Security account or by mail | Late in the year |
| Medicare Part B premium | Centers for Medicare & Medicaid Services announcement | Usually autumn |
Using the Estimate in a Budget
- Plan with a range, not a single number, until the official figure is out.
- Compare the COLA with the price changes you actually face; your own spending may rise faster or slower than the CPI-W.
- If your expenses are rising faster than your benefit, decide in advance which savings you will draw on so that you are not forced to sell investments at a bad time.
- Update your plan twice a year: once in late summer when two months of data are in, and again after the official announcement.
Common Mistakes
- Using CPI-U instead of CPI-W. The headline index is not the one in the formula.
- Using seasonally adjusted figures. The calculation uses the not-seasonally-adjusted index.
- Comparing single months. The formula averages three months.
- Forgetting deductions. Medicare premiums and withholding change what reaches your bank account.
Frequently Asked Questions
When is the 2027 COLA announced?
The Social Security Administration usually announces it in October, once the September CPI-W has been published by BLS.
What happens if prices fall?
If the third-quarter average does not rise, there is no COLA for that year. Benefits are not reduced because of a fall in the index.
Does where I live affect my COLA?
No. The COLA uses the national U.S. city average CPI-W, so it is the same percentage for everyone.
Does SSI get the same COLA?
Supplemental Security Income payment amounts are adjusted by the same COLA percentage; the Social Security Administration publishes the new amounts with its announcement.
Sources and References
- U.S. Bureau of Labor Statistics, CPI-W U.S. city average, all items, not seasonally adjusted (series CWUR0000SA0), public data API — values retrieved October 9, 2026.
- IRS Publication 915, Social Security and Equivalent Railroad Retirement Benefits.