Your paycheck gets bigger in October. January takes it back.

Social Security tax runs 6.2% from your side and 6.2% from your employer's, and the IRS describes the wage base as the maximum wage subject to the tax for that year. That last phrase is the whole mechanic. The counter starts at zero every January 1 and stops the moment your year-to-date Social Security wages reach the cap. It is not a rate that falls. It is a meter that runs out. Reach the cap and your side of the tax is finished for the year at $11,922.60, which is $483.60 more than the $11,439.00 that 2026 maxed out at.

Put a $250,000 salary on 24 semimonthly checks, $10,416.67 each. The first 18 take the full 6.2%, about $645.83 a time, and carry you to $187,500 of wages. Check 19 crosses $192,300 partway through, so only $4,800 of it is taxable and the withholding drops to $297.60. Checks 20 through 24 take no Social Security tax at all. That is about $348 back on check 19 and roughly $3,200 across the last five, arriving for no reason you did anything about.

Then January 1 resets the counter and the 6.2% restarts on dollar one. Your first check of 2027 is about $646 smaller than your last check of 2026. Same salary, same job, no letter about either event. If you want your own crossing point, do not use your salary: use the year-to-date Social Security wages line on your pay stub, because that is the figure the cap is measured against.

The common read on the cap is that earnings above it are payroll-tax free. They are not. Medicare tax has no wage base limit at all, so 1.45% keeps coming out of every dollar, in December and in January and at $400,000.

It gets slightly worse right where the cap lands. The IRS has employers withhold an extra 0.9% Additional Medicare Tax on wages above $200,000 in a calendar year, regardless of filing status, starting in the pay period you cross it and running to year end. There is no employer match on that one. So on the salary above, Social Security tax switches off at $192,300 and the surtax switches on $7,700 later. Your marginal payroll rate above the cap is 1.45%, then 2.35%, not zero, and the four checks after you pass $200,000 come in about $552 bigger rather than $646. Call it $450 of the autumn windfall handed straight back, so the real gain is closer to $3,100 than $3,550.

That $200,000 is a withholding threshold, not the tax's own threshold. The surtax actually applies above $200,000 for a single filer, $250,000 for a couple filing jointly, and $125,000 filing separately. A two-earner household can be withheld for a surtax it does not owe, or owe one nobody withheld, and settle the difference on the return.

The cap rose 4.2% for 2027. Benefits rose 3.6%. Those are not the same number because they are not measured against the same thing. The Congressional Research Service puts it plainly: since 1982 the taxable earnings base has risen at the same rate as average wages in the economy, while the COLA tracks prices. Wages and prices move at different speeds, so the two sides of the program drift apart a little every year.

One direction that drift has run for forty years: the share of all covered earnings that actually gets taxed fell from 90% in 1982 to 81% in 2021, because pay at the top grew faster than the cap did. The headcount barely moved. About 6% of covered workers earn more than the cap in a given year, 10.8 million out of 174.5 million in 2020, and CRS says that share has held near 6% since the 1980s.

Which is the honest framing here. In any single year this is a minority-of-workers story, and the 94% who never reach $192,300 pay the same 6.2% in December that they paid in March.

The practical mistake is treating the autumn bump as income. It is not a raise and it is not a bonus. It is one year's tax finishing early, and it ends on December 31. Build anything recurring on those checks, a bigger standing transfer, a new subscription, holiday spending you plan to repeat, and January arrives about $646 short. The cleanest move is the boring one: send the difference somewhere automatic for those few checks and let January feel normal.

Two cases worth knowing. If you are self-employed you pay both halves, 12.4% up to the same $192,300, which tops out at $23,845.20, and it applies to net self-employment earnings rather than what you invoiced, so your crossing point sits later than your revenue suggests. And if you changed jobs mid-year, hold your W-2s up against each other. Each employer withholds up to the cap without knowing about the other, so two jobs at $120,000 apiece will over-withhold. The IRS says that with two or more employers you may be able to claim the excess as a credit against your income tax on your return. Nobody at either company will flag it for you.