Self-Employment Tax Calculator: The 15.3% Most Freelancers Underestimate

Why the year-one surprise hits so many freelancers

When you're a W-2 employee, FICA tax (Social Security + Medicare) is 15.3% of wages — but your employer pays half, withheld invisibly before the paycheck even prints. As a 1099 worker, that "employer" is also you. Both halves come out of your pocket as Self-Employment tax. On $80,000 of net SE earnings the SE tax alone is ~$11,300 — completely separate from federal income tax. Many new freelancers budget for "income tax" and find themselves $10,000+ short come April.

The math has three small wrinkles worth knowing: (1) only 92.35% of net SE earnings is subject to SE tax (the "deduct the employer-half-equivalent" adjustment), (2) the SS portion caps at the $176,100 wage base in 2025 — earnings above that pay only the 2.9% Medicare and the 0.9% additional Medicare above $200k/$250k, and (3) half of the REGULAR SE tax (not the additional Medicare) is an above-the-line deduction from AGI, which lowers your federal income tax on the same earnings. The tool computes all three correctly.

How the math works

1. SE base = net SE earnings × 0.9235.
2. Social Security portion = 12.4% × min(SE base, $176,100). Capped at the 2025 wage base.
3. Medicare portion = 2.9% × SE base. Uncapped.
4. Additional Medicare = 0.9% × max(0, SE base − $200,000 single / $250,000 MFJ). High-earner add-on.
5. Total SE tax = SS + Medicare + Additional Medicare.
6. SE-tax deduction = (SS + Medicare) ÷ 2. Above-the-line from AGI. Additional Medicare is NOT included in the deduction.
7. AGI = net SE earnings − SE-tax deduction.
8. Federal income tax = progressive brackets on (AGI − standard deduction).
9. Total federal tax = SE tax + federal income tax.

Sources: IRS Publication 334 (Tax Guide for Small Business), Schedule SE instructions, SSA wage base table, IRS Topic 560 (Additional Medicare Tax).

What this simplifies: ignores the QBI deduction (Section 199A — up to 20% of qualified business income, can reduce federal income tax meaningfully for pass-through entities), business-expense deductions beyond what's already in the net-earnings input, state income tax, and any local SE-tax equivalents. Real SE tax planning often includes structuring as an S-corp (above ~$60-80k net) to convert some income to non-SE-taxed distributions — that's a separate calculation.

Math runs locally. Inputs never leave your browser. Source on github.

Where this calculation doesn't apply

• You're an S-corp owner-employee. S-corps split owner pay into "reasonable salary" (W-2, subject to FICA) and distributions (not subject to SE tax). At net income above ~$60-80k the S-corp structure typically saves money even after the bookkeeping/filing costs. Different math.
• You also have W-2 wages. The SS wage base is shared across your wages AND SE earnings — high-W-2-income freelancers may already hit the $176,100 ceiling and pay only Medicare on additional SE earnings. Not modeled.
• You qualify for the QBI deduction. The Section 199A deduction can reduce federal income tax (not SE tax) by up to 20% of qualified business income, with phaseouts above income thresholds. Materially changes the total tax for many pass-through businesses.
• Special tax situations. Statutory employees, ministers, farmers, and a handful of other classifications have different SE-tax rules. Consult a CPA.

What to actually do

1. Set aside the effective rate shown × every invoice as you receive it — into a separate account. Tax-time surprises happen because the cash already got spent.
2. Pay quarterly estimated tax (see the related tool). The IRS will assess an underpayment penalty even if you pay everything by April 15.
3. Track business expenses meticulously. Every dollar reduces both SE tax (via lower net earnings) and federal income tax — double-decker savings.
4. At net income above $60-80k, ask a CPA whether an S-corp election would save money on net after the added bookkeeping cost.