How the Social Security COLA Is Determined
The cost-of-living adjustment (COLA) effective for December 2026 is 3.6 percent. It comes out of a formula written into the Social Security Act. That formula runs on an index called the Consumer Price Index for Urban Wage Earners and Clerical Workers (CPI-W).
Social Security benefits will increase by 3.6 percent beginning with the December 2026 benefits, which are payable in January 2027. Under the Social Security Act’s formula, COLAs are based on increases in the CPI-W. Because of rounding, possible offsets, and final truncation, the increase in a monthly retirement benefit over the previous amount may differ somewhat from the COLA.
What the COLA Formula Compares
SSA puts the purpose in one line: with COLAs, Social Security and Supplemental Security Income (SSI) benefits keep pace with inflation. The Social Security Act specifies a formula for determining each COLA, and according to that formula, COLAs are based on increases in the CPI-W. CPI-Ws are calculated on a monthly basis by the Bureau of Labor Statistics.
SSA’s announcement of the 3.6 percent increase also describes the formula. The Social Security Act provides for how the COLA is calculated. It ties the annual COLA to the increase in the CPI-W, as determined by the Department of Labor’s Bureau of Labor Statistics.
The formula measures the percentage increase, if any, in the average CPI-W for the third quarter. The starting point is the third quarter of the last year in which a COLA became effective. The end point is the third quarter of the current year.
A COLA set this way is effective for December of the current year. If there is an increase, it must be rounded to the nearest tenth of one percent. If there is no increase, or if the rounded increase is zero, there is no COLA for the year.
The Third-Quarter Numbers Behind 3.6 Percent
For the COLA effective for December 2026, the last year in which a COLA became effective was 2025. The law therefore requires using the average CPI-W for the third quarter of 2025 as the base from which the increase, if any, is measured. That base average is 317.265.
The average CPI-W for the third quarter of 2026 is 328.746. Because this average exceeds 317.265 by 3.6 percent, the COLA effective for December 2026 is 3.6 percent. Rounded to the nearest one-tenth of one percent, the arithmetic is this: (328.746 - 317.265) / 317.265 x 100 = 3.6 percent.
SSA publishes the monthly CPI-W figures for 2025 and 2026 that make up both averages.
| CPI-W for— | 2025 | 2026 |
|---|---|---|
| July | 316.349 | 327.104 |
| August | 317.306 | 328.481 |
| September | 318.139 | 330.654 |
| Third quarter total | 951.794 | 986.239 |
| Average (rounded to the nearest 0.001) | 317.265 | 328.746 |
Source: Social Security Administration
Three months on one side, three months on the other. Each average in SSA’s table is rounded to the nearest 0.001.
When the Increase Reaches Payments
SSA announced the 3.6 percent benefit increase on Wednesday, October 14, 2026. The announcement says Social Security benefits include Old-Age, Survivors, and Disability Insurance (OASDI) and Supplemental Security Income (SSI). Nearly 72 million Social Security beneficiaries will see a 3.6 percent COLA beginning in January 2027.
Increased payments to about 7.3 million people receiving SSI will begin on December 31, 2026. Some people receive both Social Security benefits and SSI.
Social Security benefits will increase by 3.6 percent beginning with the December 2026 benefits, which are payable in January 2027. Federal SSI payment levels will also increase by 3.6 percent effective for payments made for January 2027.
The normal SSI payment date is the first of the month, and January 1 is a holiday. So the SSI payments for January are always made at the end of the previous December.
On average, Social Security retirement benefits will increase by $75 per month.
People with personal my Social Security accounts can view their COLA notice online starting in late November. That is up to three weeks earlier than a paper notice in the mail.
Account holders can also choose to receive text or email alerts when a new message is available in their account’s Message Center. The COLA notice is one of those messages.
For people without a personal account, seeing the COLA notice online requires creating one and enrolling in paperless notices by November 18. People who have not enrolled in paperless notices will receive their COLA notice by mail in December.
Social Security beneficiaries will receive a simplified, one-page COLA notice. It provides exact dates and dollar amounts of an individual’s new benefit amount and any deductions. For Medicare enrollees, the 2027 premium amount will be available via the my Social Security Message Center starting in late November.
From the PIA to the Monthly Benefit
Here the round percentage stops being round. A COLA increases a person’s Social Security retirement benefit by approximately the product of the COLA and the benefit amount. The exact computation, however, is more complex.
Each Social Security benefit is based on a primary insurance amount (PIA), which is directly related to the primary beneficiary’s earnings through a benefit formula. It is the PIA that is increased by the COLA, with the result truncated to the next lower dime.
SSA offers an example. The initial PIA is $2,197.50 and it is increased by a 3.6-percent COLA. The new PIA would be $2,276.60 after truncation to the next lower dime.
Retiring before normal retirement age makes the benefit lower than the PIA, and retiring after normal retirement age makes it higher. A factor is applied to the PIA to account for early or delayed retirement, with the result truncated to the next lower dime.
When a COLA occurs, SSA increases the PIA and repeats the steps required to calculate the new benefit amount based on the new, higher PIA. Because of rounding, possible offsets, and final truncation, the increase in the new monthly benefit over the previous amount may differ somewhat from the COLA.
The Fund Ratio Condition in the Law
One more condition sits in the statute, and SSA restates it in its published cost-of-living determination.
Section 215(i) of the Social Security Act specifies a limit on a benefit increase under title II, effective for December of any year. The limit applies if the OASDI fund ratio for that year is below 20.0 percent. The increase is then limited to the increase in the national average wage index for the prior year.
The OASDI fund ratio for a year is the ratio of two amounts. One is the combined asset reserves of the OASI and DI Trust Funds at the beginning of that year. The other is the combined cost of the programs during that year.
Decisions that depend on one person’s benefit figures are a matter for a qualified professional.
Social Security benefits reflect the 3.6 percent beginning with the December 2026 benefits, payable in January 2027. SSI payments for January 2027 are paid on December 31, 2026.
That 3.6 percent came from comparing two third-quarter CPI-W averages and rounding the result. The fund ratio condition sits in the same section of the law.
This article is general information, not professional advice. For decisions about your money or health, consult a qualified professional.