The two taxes, side by side
| Social Security (OASDI) | Medicare (HI) | |
|---|---|---|
| Employee rate | 6.2% | 1.45% |
| Employer rate | 6.2% | 1.45% |
| Self-employed | 12.4% | 2.9% |
| Wage limit in 2027 | $192,300 | None |
| Additional surtax | None | 0.9% above $200,000 / $250,000 |
What you see on a pay stub
Withholding is applied to cumulative wages. Once year-to-date pay passes the Social Security wage base, that line becomes zero for the rest of the year. The Medicare line does not change, because there is no cumulative threshold to cross.
This is why a high earner’s take-home pay jumps in the last months of the year: one tax disappears and the other keeps running at the same rate.
The surtax is easy to miss
The additional 0.9% is not part of the 1.45% rate and is not matched by an employer. It applies to wages above $200,000 for a single filer and $250,000 for a married couple filing jointly. Those thresholds are fixed by statute, so more people cross them each year purely through wage growth.
If you have two jobs, each employer applies the threshold to its own payroll only. You may owe the surtax at filing even if neither employer withheld it.