Guide · Social Security & Medicare
How Medicare Part B eats into your Social Security COLA
Each fall you learn two numbers close together: your Social Security cost-of-living raise, and your new Medicare Part B premium. Because Part B is usually pulled straight out of your Social Security check, those two numbers land in the same place — your monthly deposit. This guide shows, in plain terms, why your raise can feel smaller than the headline, and how to figure out the amount you actually keep.
Illustrative estimates only CMS sets the standard Part B premium each fall; the 2027 COLA is announced October 14, 2026.
Why the two are linked
For most people, the Medicare Part B premium isn't a separate bill you pay by hand. It's withheld directly from your Social Security payment before the money reaches your bank. Social Security sends the premium to Medicare on your behalf, and you receive what's left.
That's why a raise and a premium increase collide. Every autumn, two things happen within a few weeks of each other: Social Security announces the year's cost-of-living adjustment (COLA), and Medicare sets the new standard Part B premium. Both changes take effect in January, and both show up on the very same deposit. So even though your benefit went up by the full COLA, the number you actually see arrive can grow by less — because a bigger slice was taken out for Part B on the way through.
Understanding that hand-off is the whole trick. Your gross benefit and your net deposit are two different figures, and the gap between them is Part B.
The math, plainly
There's really just one formula to keep in mind. It's the same subtraction our COLA calculator does for you:
The one formula that matters
Net deposit = (your current benefit × (1 + COLA)) − your Medicare Part B premium.
Let's walk through it with round, illustrative numbers. Say your current monthly benefit is $2,000, and we apply the 2027 estimated COLA of 3.6%. Remember: that 3.6% is an early estimate, not the official figure, and the Part B amounts below are round illustrations, not a premium CMS has announced.
| Step | Amount |
|---|---|
| Current monthly benefit (before Part B) | $2,000.00 |
| Gross raise ($2,000 × 3.6%) | +$72.00 |
| New monthly benefit (gross) | $2,072.00 |
| Illustrative Part B premium this year | −$185.00 |
| Illustrative Part B premium next year | −$200.00 |
| Deposit this year ($2,000 − $185) | $1,815.00 |
| Deposit next year ($2,072 − $200) | $1,872.00 |
| Raise you actually keep ($1,872 − $1,815) | +$57.00 |
Every dollar figure above is a round, made-up illustration to show how the subtraction works. The $185 and $200 Part B amounts are not official — CMS sets the real standard premium each fall, and the 3.6% COLA is an early estimate until the Social Security Administration announces the official number on October 14, 2026.
Notice the two figures the example produces. The gross raise was $72 a month. But because Part B also went up — from $185 to $200 in this illustration — the raise you keep was only $57. The $15 Part B increase quietly clawed back part of the COLA. Your benefit still rose by the full 3.6%; your deposit rose by less. That gap is the entire point of this page.
The hold-harmless provision
There's an important protection built into the law, and it has a slightly stuffy name: the hold-harmless provision. In plain terms, it means that for most people, the dollar increase in the Part B premium can't be larger than the dollar increase in their Social Security benefit. Put simply: your net Social Security deposit shouldn't go down from one year to the next just because Part B went up.
Here's the idea. If your COLA raise is small in dollar terms and the Part B increase would have been larger, hold-harmless caps the Part B increase so it never wipes out your raise and pushes your deposit backward. Part B can eat into your COLA — but for people who are protected, it can't eat past it and leave you with a smaller check than the year before.
Good to know
Hold-harmless protects most people who have Part B withheld from their Social Security check, but it doesn't cover everyone. People new to Medicare, those who don't yet receive Social Security, and higher-income beneficiaries who pay an income-related surcharge are among those it may not fully shield. If you're unsure, the official Medicare and Social Security sites explain how it applies to you.
A quick word on IRMAA
Most people pay the standard Part B premium. But if your income is above a certain level, you pay more — an extra amount on top of the standard premium for both Part B and Part D. This surcharge is called IRMAA (the Income-Related Monthly Adjustment Amount). It's based on the income reported on your tax return from a couple of years back, and it climbs in steps as income rises. If IRMAA applies to you, your Part B deduction is larger, so a bigger slice of your COLA can be absorbed. The specific income thresholds change each year and are set by the government, so check the official sources for the figures that apply to your situation rather than relying on last year's numbers.
See it for your own check
The clearest way to understand this is to run your own numbers instead of ours. Our calculator applies the COLA to your benefit and then subtracts Part B — including next year's premium if you know it — so you see the gross raise and the amount you actually keep, side by side. Nothing you type ever leaves your device.
Do this subtraction for me
Enter your benefit and Part B premium, and see your 2027 raise before and after Part B is taken out.
Open the COLA calculator →How the COLA itself works
Where the 2027 estimate comes from, the CPI-W formula, and a worked example — in plain language.
Read the COLA guide →Frequently asked questions
Why did my Social Security deposit go up by less than the COLA?
Because Medicare Part B is usually withheld from your payment before it reaches your bank. Your gross benefit rises by the full COLA, but if the Part B premium also increases, the change to your actual deposit is smaller. The difference between those two numbers is exactly what our COLA calculator makes visible.
What is the standard Part B premium this year?
CMS sets the standard Part B premium each fall, and it can change from year to year. We don't publish a fixed dollar figure here because it's official government information that's updated annually — check the current amount on the official Medicare site, or look at what's withheld from your own Social Security statement, and enter that number in our calculator.
Can Part B ever make my check smaller than last year?
For most people, no. The hold-harmless provision generally prevents the dollar rise in Part B from exceeding the dollar rise in your Social Security benefit, so your net deposit shouldn't drop just because Part B went up. It doesn't cover everyone, though — people new to Medicare and higher-income beneficiaries who pay the IRMAA surcharge may not be fully protected.
What is IRMAA?
IRMAA is the Income-Related Monthly Adjustment Amount — an extra charge added to the standard Part B and Part D premiums for people with higher incomes. It's based on your tax return from a couple of years earlier and rises in steps as income increases. If it applies to you, your Part B deduction is larger, so more of your COLA can be absorbed. The income thresholds are set by the government and change each year.
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