Self-employment tax catches most new freelancers off guard. When you work a regular job, your employer quietly pays half of your Social Security and Medicare taxes (7.65%) and withholds the other half from your paycheck. When you go solo, both halves are yours: 12.4% Social Security on earnings up to the annual wage base, plus 2.9% Medicare on every dollar, for a combined 15.3% on the first chunk of net income.
That number sounds brutal — and it is — but the actual mechanics give you several breaks. SE tax is calculated on 92.35% of net earnings, not 100%. Half of the SE tax you pay is deductible on your federal return as an above-the-line adjustment. And the Social Security portion stops once you cross the annual wage base (currently around $168k+ and rising). Use the Self-Employment Tax Calculator to see all three of those mechanics applied to your numbers in real time.
Who actually owes SE tax
You owe self-employment tax if your net earnings from self-employment are $400 or more in a year. That includes 1099 contract work, freelance projects, single-member LLC income, partnership distributions, and side-hustle income reported on Schedule C. It does not include W-2 wages (those already had FICA withheld), most rental income, or qualified dividend/interest income.
How SE tax interacts with income tax
SE tax and federal income tax are calculated separately and stacked. A freelancer in the 22% federal bracket earning $80k net is looking at roughly 15.3% SE tax + 22% marginal income tax + state tax — easily 35-45% on the next dollar earned. The 1099 Tax Calculator shows the full stack for any state and filing status, and the Freelance Rate Calculator reverse-engineers the hourly rate you need to charge to net a target income after all of it.
Quarterly payments and the safe harbor
Because no employer is withholding for you, the IRS expects four estimated payments per year. The safest approach is the "100% / 110% safe harbor" — pay at least 100% of last year's total tax (110% if your AGI was over $150k) in equal quarterly installments and the IRS cannot penalize you, even if this year's income explodes. The Self-Employment Tax Guide walks through the worksheet step by step.
The single biggest mistake to avoid
Treating revenue like income. A $10,000 invoice is not $10,000 of take-home — after SE tax, federal, state, and the deductions you forgot to track, the actual deposit into your savings account is closer to $5,500-6,500 for most freelancers. Build the habit of moving 25-35% of every payment into a separate tax savings account the day it lands. By April you will have the cash already set aside instead of scrambling.