Understanding Self-Employment Taxes: A Comprehensive Guide
Self-employment tax is the single biggest surprise for people who go independent. You leave a W-2 job, start freelancing or run your own S-Corp, and suddenly there's a tax bill that's bigger than anything you saw as an employee, or worse, a penalty because nobody told you it's due quarterly, not once a year.
Here's what it actually is, how it's calculated down to the dollar, and the one real structural change that legally reduces it.
What is self-employment tax?
When you're a W-2 employee, Social Security and Medicare taxes get split between you and your employer, 7.65% each, 15.3% combined. When you're self-employed, there's no employer to split it with. You're both sides of that transaction, so you owe the full 15.3% yourself.
That's self-employment tax: the combined Social Security and Medicare tax self-employed people pay on their net business income, on top of regular income tax, not instead of it.
How is self-employment tax actually calculated?
Here's the math, step by step:
Start with net self-employment income. Revenue minus allowable business expenses.
Social Security portion: 12.4%, up to the annual wage base limit. For 2026, that limit is $184,500. Income above that isn't subject to this portion.
Medicare portion: 2.9%, on your entire net earnings, no cap. An additional 0.9% Medicare surtax kicks in above $200,000 for individuals or $250,000 for married couples filing jointly.
Add those together and you get the full 15.3% self-employment tax rate.
Quick example: on $100,000 of net self-employment income, that's roughly $14,130 in self-employment tax alone, before regular income tax even enters the picture. That's the number that catches people off guard.
For the government's own explanation of how the Social Security portion works, the SSA's guide to self-employment taxes breaks down the wage base and benefit calculation in detail.
Who owes self-employment tax?
Anyone with net self-employment income of $400 or more: sole proprietors, independent contractors, freelancers, all of it.
How to pay it
Self-employed workers make estimated quarterly payments, roughly due in January, April, June, and September, based on expected income for the year. Miss a quarter and you're looking at penalties and interest, not just a bigger bill later.
Self-employment income and tax get reported on Schedule SE (Form 1040), filed alongside your annual return.
Opolis handles withholding and remittance automatically for Employee Members through W-2 payroll built for solopreneurs, so this isn't a quarterly fire drill on a spreadsheet.
The one real way to reduce it
Here's the part most freelancers don't find out until later: electing S-Corp status changes what portion of your income is even subject to self-employment tax.
As a sole proprietor or default LLC, all of your net income is exposed to the full 15.3%. As an S-Corp, you split income into two buckets: a reasonable salary (taxed the same as before) and distributions (not subject to self-employment tax at all). For a deeper look at how distributions are taxed differently from salary and bonus pay, see our breakdown of K-1 distributions vs. bonus vs. regular payroll.
Worked example: say your business nets $100,000. As a sole proprietor or default LLC, the full $100,000 is subject to the 15.3%, roughly $14,130 in self-employment tax. As an S-Corp, if a reasonable salary for your work is $60,000, only that $60,000 gets taxed at 15.3%, about $8,478, while the remaining $40,000 comes out as a distribution with no self-employment tax at all.
That roughly $5,600 difference is where the commonly cited "S-Corp owners save $5,000 or more a year" figure actually comes from. It's not a loophole, it's the structural difference in how the two entity types are taxed.
The trade-off: S-Corp status adds real administrative weight, actual payroll with withholding and W-2s, a wage the IRS would consider "reasonable," and additional filing. That overhead is exactly what Opolis's W-2 payroll structure is built to absorb, including the updated S-Corp vs. C-Corp breakdown if you're still deciding between structures, so the tax savings aren't offset by a part-time job running your own payroll.
Deductions worth knowing
Self-employed individuals qualify for deductions that reduce taxable income, including business expenses, home office costs, and health insurance premiums. The self-employed health insurance deduction is one people commonly miss, and it stacks with group medical coverage available through membership.
FAQ
How much is self-employment tax? 15.3% of net self-employment income: 12.4% Social Security (up to the annual wage base limit) plus 2.9% Medicare (uncapped).
Do I pay self-employment tax and income tax? Yes, both. Self-employment tax covers Social Security and Medicare specifically. Regular income tax is calculated separately, on top of it.
Does an S-Corp pay self-employment tax? Not in the traditional sense. S-Corp owner-employees pay standard payroll taxes on their salary, but the distribution portion of their income isn't subject to the 15.3%, which is the piece a sole proprietor can't separate out.
Can I avoid self-employment tax entirely? Not if you're earning self-employment income, but electing S-Corp status reduces how much of it is exposed to the 15.3%.
Conclusion
Understanding self-employment tax is the difference between a manageable quarterly payment and a bill you weren't ready for. Once you know how it's calculated, the S-Corp election stops being an abstract tax strategy and becomes a concrete number you can weigh against the added payroll overhead. If you haven't set up your entity yet, you'll need an EIN first, make sure you meet the minimum earnings requirements for membership, and check your eligibility once you're ready to make the S-Corp election real.