A Social Security cost-of-living adjustment can raise the benefit amount on the books without raising every beneficiary's bank deposit by the same percentage. The gap opens after the gross benefit is calculated. Premiums, withholding and other deductions change what reaches the account.
What the COLA actually changes
The cost-of-living adjustment, or COLA, changes the gross Social Security benefit. "Gross" means the benefit before deductions. The deposit is the net amount left after deductions and offsets. A COLA is therefore no promise that each deposit will rise by the same percentage.
The 2026 COLA was 2.8%, according to the Center for Retirement Research. The source behind this article cites a 3.6% COLA and labels it the 2027 adjustment. Readers should confirm that figure and its effective date against the Social Security Administration's own announcement before relying on it. The percentages below are used only to show how the mechanics work.
By law, SSA bases the COLA on the change in the third-quarter average of the Consumer Price Index for Urban Wage Earners and Clerical Workers, known as CPI-W. The formula applies to benefit amounts under statutory rules, including rounding inside the benefit computation. Multiplying an old deposit by 1.036 is not a reliable way to find a new one. The deposit carries deductions that the gross-benefit formula never touches. One explainer on the 3.6% COLA walks through this difference. It is a commercial blog, so check the rules themselves with SSA.
Why a deposit can rise by less
Medicare Part B premiums are the most visible reason. When the premium is taken out of a Social Security payment, a higher premium absorbs part of the COLA gain. CMS lists the 2026 standard Part B premium at $202.90 a month, up from $185 in 2025. That is a rise of nearly 10%. The same CMS fact sheet for 2026 shows the Part B deductible rising to $283.
The Center for Retirement Research estimates that the 2026 Part B increase will consume more than a quarter of the 2.8% COLA. It also projects that Part B premiums will equal 9.4% of the average Social Security benefit in 2026, up from 8.3% in 2018. Its analysis is available on its site. These are averages. An individual's result depends on the individual's own deductions.
Higher earners may also pay an income-related monthly adjustment amount, or IRMAA, on top of the standard premium. Under the 2025 table in the CMS 2025 fact sheet, a single filer with modified adjusted gross income above $106,000 and up to $133,000 paid a total Part B premium of $259.00. CMS says these adjustments affect roughly 8% of people with Part B. The sources reviewed here do not give the 2027 premium or IRMAA thresholds. Those need to come from the relevant CMS notice once it is published.
Other deductions that move the deposit
Premiums are not the only line on a notice. Federal income-tax withholding may go up or down. An overpayment recovery or a court-ordered garnishment may appear or change. An optional deduction may also change. Each one sits between the gross benefit and the deposit, and none is tied to the COLA.
That is why a smaller deposit increase does not, by itself, show that SSA applied the wrong COLA. A deduction may have grown enough to shrink the net gain or cancel it. The cause is usually on the notice, as a changed line item.
The sources do not give household-level deduction amounts. They do not explain how an overpayment recovery is calculated or how to dispute one. For a specific line item, the notice and SSA are the places to ask.
How to check the numbers
Compare like with like. Put the old gross benefit next to the new gross benefit. Then put the old net payment next to the new one. Starting from two bank deposits mixes the COLA with every deduction that changed in the same period.
A simple worksheet is enough. Write down the gross benefit on the earlier notice and on the newer one. Then list each deduction, old and new:
- Medicare Part B premium and any IRMAA amount
- Federal tax withholding
- Overpayment recovery or garnishment
- Optional deductions
If the gross benefit rose by the stated COLA but the deposit rose by less, the deduction comparison may explain the gap. If the gross figures themselves do not reflect the stated adjustment, that is a different question. Keep the two comparisons apart before drawing a conclusion.
Separate a formula question from an index debate
Three issues can sound alike. One is whether the CPI-W formula was applied correctly. Another is whether CPI-W is the best index for a particular group. The third is whether a change in deductions reduced the deposit. A disagreement about the index does not establish an arithmetic error in a benefit calculation.
The Bureau of Labor Statistics publishes R-CPI-E, a research index with spending weights for Americans age 62 and older. BLS describes it as a research series with sampling, outlet, item and discount limitations. It is not the index used for the official COLA. The sources do not say how often it is published or whether it could replace CPI-W. It shows that inflation measures can differ. It does not show what any one retiree should have received.
Proposals to change the formula exist too. AARP's Public Policy Institute has written about a flat-rate COLA that would replace the current formula with a fixed annual increase, and it says benefits would be cut over time. That is a policy debate. It has no bearing on how a current notice is calculated.
A better first question than "Did my deposit rise by the COLA?" is this one: did the gross benefit change as expected, and what changed in the deductions? The answer separates the benefit calculation from the net payment.
Please seek a professional. This article is general information, not financial, tax or insurance advice. Please seek a licensed financial, tax or insurance professional about your own situation.
