Double Taxation on Medicare and Social Security?
Course: Income Tax Planning
Lesson 7: Arriving at Adjusted Gross Income
Student Question:
Am I correct that this looks like paying taxes over taxes by first adding the 2.9% for Medicare taxes, and then paying Social Security tax over that?
“3. Calculate self-employment tax:
- If step 2 is less than or equal to the SSTWB, multiply by 15.3%.
- If step 2 is greater than the SSTWB, multiply step 2 by 2.9% and add that total to the SSTWB x 12.4%?”
Instructor Response:
Hi
This is a really common point of confusion, so you’re not alone — but no, it’s not paying “taxes on taxes.”
What’s happening is that self-employment tax is actually two separate taxes layered together:
- 12.4% Social Security tax, which applies only up to the Social Security taxable wage base (SSTWB)
- 2.9% Medicare tax, which applies to all net earnings from self-employment, with no cap
When net earnings are at or below the SSTWB, both taxes apply to the same income, so they’re combined into a single 15.3% rate (12.4% + 2.9%).
When net earnings exceed the SSTWB, the calculation splits:
- 12.4% is applied only to income up to the wage base
- 2.9% is applied to all earnings, including the amount above the wage base
So the formula isn’t taxing one tax on top of another — it’s simply applying different taxes to different portions of the same income, each according to its own rule.
A helpful way to think about it is:
Social Security has a ceiling, Medicare does not.
