2027 COLA vs Medicare Part B: the projected $209.50 premium math

When the 2027 cost-of-living adjustment is announced in mid-October, the headlines will report a single percentage. Retirees will not see that percentage in their bank balance. Three deductions stand between the announced COLA and the deposit that actually arrives: the Medicare Part B premium, a rounding rule that always moves against you, and whatever tax withholding you have elected on Form W-4V. The first of those three, and by far the largest, now has a government projection attached to it.

The short answer. The 2026 Medicare Trustees Report projects the standard Part B premium will rise to $209.50 a month in 2027, up $6.60 from the current $202.90. Because Part B is deducted directly from the Social Security check, that $6.60 comes off the top of the COLA before the money ever reaches the bank. Run it against the 2027 COLA tracker’s current center-of-range estimate of 3.4 percent, and a $2,000 monthly benefit gets a gross raise of $68.00 — but the deposit only rises by $61.40, because Medicare claims $6.60 of it before the math is done.

How much of the COLA Medicare actually claims

The $6.60 premium increase is a flat dollar figure, so it does not scale with your benefit. That single fact means the percentage of your raise that Medicare absorbs depends heavily on how large your check already is. Using the 3.4 percent scenario from the tracker:

Monthly benefit	COLA raise (3.4%)	Real deposit increase	Absorbed by Part B
$1,200	$40.80	$34.20	16.2%
$2,000	$68.00	$61.40	9.7%
$3,000	$102.00	$95.40	6.5%

The pattern is the whole lesson: the smaller the benefit, the larger the share of the raise that disappears into the Part B premium. A retiree living on $1,200 a month loses roughly a sixth of their announced increase before it touches their account; a retiree on $3,000 loses about a fifteenth. If the COLA lands below 3.4 percent, the arithmetic gets worse for everyone — at 2.5 percent, a $2,000 benefit gains $50.00 gross but only $43.40 net, with Part B taking 13.2 percent. At 3.5 percent, the top of the tracker’s current range, the same benefit gains $70.00 gross and $63.40 net, with Part B down to 9.4 percent of the raise. A larger COLA does not just mean a bigger check; it mechanically shrinks the share Medicare takes, because the premium increase stays fixed while the raise grows around it.

The projection has a track record, and it is decent but not exact

It is worth being direct about what $209.50 actually is: a projection published by the Trustees, not a number CMS has set. The same table in the report, Table V.E2, lists $202.90 and $283 for 2026 — and those turned out to be exactly what CMS published in the Federal Register on November 19, 2025. That is a strong track record for the row this analysis leans on. But the prior year’s report was less precise: the 2025 Trustees Report projected $206.50 for 2026, which came in $3.60 above the actual $202.90 CMS later announced. The report itself is candid about this, stating plainly that “these values are estimates, and the actual amounts are likely to be somewhat different as experience emerges.” The honest takeaway is that $209.50 is a serious, government-produced number worth planning around, not a number to treat as final until CMS confirms it in November 2026.

The second deduction: rounding always goes down

Even before Medicare and taxes enter the picture, federal law shaves a few cents off every COLA-adjusted benefit. Under 42 U.S.C. § 415(i), any resulting benefit that is not an even multiple of $0.10 gets rounded down to the next lower dime — never up, and never to the nearest cent. The effect is small on any single check but permanent every month after. A benefit of $1,847.30, multiplied by a 3.4 percent COLA, comes to $1,910.11 to the cent. The rounding rule drops that to $1,910.10 — a difference of less than a cent this time, but the same permanent loss repeats every month until the next adjustment, whatever its size.

The third deduction: whatever withholding you chose

Anyone who filed Form W-4V to have federal taxes withheld from Social Security is applying that percentage — 7, 10, 12, or 22 percent, a fixed menu that works nothing like the W-4P steps a pension uses — to the gross benefit, which means withholding also eats into the COLA increase, not just the base payment. Take a $2,000 benefit with 10 percent withholding elected, under the 3.4 percent COLA and the projected Part B premium. The 2026 deposit works out to $2,000 minus $202.90 in Part B minus $200.00 in withholding, or $1,597.10. The 2027 deposit is $2,068.00 minus $209.50 minus $206.80, or $1,651.70. The real increase in what reaches the bank is $54.60 — noticeably less than the $61.40 a beneficiary with no withholding would see on the identical $2,000 benefit and the identical COLA. Withholding is optional and often sensible for tax planning, but it is one more percentage applied to a bigger number, which means a bigger dollar amount disappears from the raise.

Where hold-harmless does and does not apply

Some readers will recall a legal backstop that is supposed to prevent a Medicare premium hike from ever shrinking a Social Security check. That protection, the hold-harmless provision, only stops the dollar amount of the check from falling — it does not stop Medicare from absorbing most or nearly all of a raise. With the projected $6.60 premium increase and a 3.4 percent COLA, only benefits below roughly $194 a month ($6.60 divided by 0.034) would even be at risk of triggering the protection. At the COLA levels currently in the tracker’s range, almost no one qualifies for hold-harmless in 2027 — the projected premium increase is small enough, and the projected COLA large enough, that checks rise for nearly every beneficiary, just by less than the headline percentage suggests.

What to do with this before November

None of the numbers above are final. The $209.50 premium is a Trustees Report projection, not a CMS announcement — that arrives in November 2026. The COLA itself is not known until mid-October, when the Bureau of Labor Statistics publishes the September CPI-W; the 2027 COLA tracker follows that data as it lands. Once the percentage is announced, the practical next question for most beneficiaries is not the raise itself but when it shows up — covered in our guide to the first 2027 COLA payment date. Higher earners should also check whether their income crosses a Medicare surcharge threshold, since the 2027 IRMAA brackets projection adds a separate, income-based premium on top of the standard $209.50 used throughout this analysis. Until CMS confirms the real premium, the arithmetic here is the best available planning number, built on a Trustees Report row that matched CMS exactly last year — and came within a few dollars the year before that.