Medicare & Social Security Explained: How the Two Taxes Differ

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Social Security and Medicare get lumped together on your pay stub under "FICA," but they're two different programs with two different tax structures. One has a ceiling. The other doesn't. One is matched dollar-for-dollar by your employer at every income level. The other, past a certain point, isn't. Knowing the difference matters if you're checking your own math, projecting a raise, or trying to understand why a bonus check withheld more than you expected.

Social Security: Capped by Design

Social Security tax is 6.2% of your wages, withheld from your paycheck, with your employer paying a matching 6.2% on your behalf — 12.4% total. That money funds retirement, disability, and survivor benefits, and your future benefit amount is calculated from your recorded earnings history.

The tax only applies up to an annual wage base — a dollar ceiling that adjusts every year. Once your year-to-date wages cross that line, Social Security withholding stops for the rest of the year, even though your paycheck keeps coming. This is why a high earner's take-home pay sometimes jumps mid-year: one deduction simply disappears. If you switch jobs mid-year, this can get more complicated, because each employer tracks the cap independently, and any resulting overpayment gets reconciled when you file your return.

Medicare: No Ceiling, But a Surtax

Medicare tax is 1.45% from you and 1.45% from your employer — 2.9% combined — and it applies to every dollar of wages, with no annual cap. It funds hospital insurance coverage for people 65 and older and certain people with disabilities.

The wrinkle is the Additional Medicare Tax. Once your wages for the year exceed $200,000, your employer must withhold an extra 0.9% on the amount above that threshold. This additional withholding is not matched — your employer never pays a corresponding share of it. It's also calculated per employer, based only on wages that specific employer paid you, so if you have two jobs that individually stay under $200,000 but together exceed it, you may owe more Additional Medicare Tax on your return than either employer withheld.

Side-by-Side Comparison

| | Social Security | Medicare | |---|---|---| | Employee rate | 6.2% | 1.45% (+0.9% above $200,000) | | Employer rate | 6.2% | 1.45% (no match on the 0.9%) | | Wage cap | Yes, adjusts annually | No cap | | Funds | Retirement, disability, survivor benefits | Hospital insurance (Part A) |

For a plain-English intro to how these two combine into what shows up as "FICA" on your stub, see the FICA tax overview. If you're trying to locate and verify these specific lines on your own stub, see FICA on your pay stub.

A Worked Example

Take a salaried employee earning $180,000 a year, paid semi-monthly (24 pay periods), so gross pay per check is $7,500.

• Social Security (6.2%): $465.00 per check, as long as year-to-date wages stay under the annual cap
• Medicare (1.45%): $108.75 per check
• Combined FICA per check: $573.75

Now assume that same employee gets a $50,000 bonus added to their December paycheck, pushing year-to-date wages past $200,000. The portion of that check above $200,000 gets an extra 0.9% Medicare withholding on top of the standard 1.45% — a detail that catches people off guard because nothing about their salary changed, only the timing of a bonus.

Why the Structures Are Different at All

Social Security is designed as an earned-benefit program: what you receive later is tied to what you paid in, up to a maximum benefit. Capping the tax caps the benefit calculation on the back end too, which is why the wage base isn't arbitrary — it's built into the same formula that eventually determines your monthly check. Medicare, by contrast, provides essentially the same hospital insurance coverage to everyone at retirement age regardless of lifetime earnings, so there's no actuarial reason to cap the tax that funds it. The Additional Medicare Tax exists purely as a revenue measure layered on top, not as a benefit-linked calculation, which is part of why it isn't employer-matched the way the base rate is.

Self-Employed: You Pay Both Sides

If you work for yourself, there's no employer to split either tax with, so you pay the full combined rate — the equivalent of both the employee and employer shares — as self-employment tax. That's effectively 12.4% for Social Security up to the same annual wage base, and 2.9% for Medicare with no cap, plus the same 0.9% Additional Medicare Tax above $200,000 in net earnings. The wage base and Additional Medicare Tax threshold rules work the same way; only the fact that you're covering both halves changes. For how this affects your income documentation, see proof of income for self-employed workers and 1099 income basics.

The Bottom Line

Social Security and Medicare share a name on your pay stub but not a rate structure. Social Security is capped and benefit-linked; Medicare is uncapped and adds a surtax for high earners that isn't matched. Once you separate the two, checking your withholding — or explaining a paycheck that suddenly looks different — becomes a matter of simple arithmetic instead of guesswork.

Frequently Asked Questions

Related Guides

• FICA Tax Explained
• FICA on Your Pay Stub
• How Payroll Taxes Work

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Authoritative source: IRS — Topic 751: Social Security & Medicare Withholding Rates

This guide is informational and not legal or tax advice.