One ceiling, and one thing with no ceiling
Payroll tax is two separate taxes that happen to be withheld together. The Social Security part applies to wages up to an annual taxable maximum. The Medicare part applies to every dollar, with no upper limit at all.
So for anyone earning more than the maximum, the two behave completely differently partway through the year. The Social Security line on a payslip stops. The Medicare line does not, and never will.
Why a paycheck gets bigger in the autumn
Someone whose pay passes the taxable maximum in, say, September sees their take-home rise from that point, with no raise and no change in withholding elections. Nothing has happened except that one of the two payroll taxes has finished for the year.
It resets in January. The rise is not permanent and it is not a pay increase, which is worth knowing before budgeting around it. Our wage base calculator shows where in the year a given salary crosses the maximum.
The maximum moves every year
It is adjusted annually in line with average wage growth, and the figure is published by the Social Security Administration each autumn alongside the cost-of-living adjustment. The rate itself has not changed in decades; it is the ceiling that moves.
That is why a calculator for this has to be tied to a year rather than to a number. The rules are stable and the threshold is not.
What this does not cover
Self-employment. Under SECA the same two taxes apply at double the rate, because a self-employed person pays both the employee and the employer half, and they apply to a slightly reduced measure of net earnings rather than to wages. That is a different calculation and we do not currently show it rather than approximate it.
There is also a third payroll tax above a much higher threshold: the Additional Medicare surtax, which is employee-only and has its own rules about which wages count.