Self-Employment Tax and Quarterly Payments, Explained

Anyone who goes from a W-2 job to freelancing tends to have the same moment of sticker shock: self-employment tax. It's the 15.3% combined Social Security and Medicare tax you owe on net profit, on top of ordinary federal income tax: money an employer would otherwise split with you through payroll withholding that a freelancer has to cover alone.

How Self-Employment Tax Is Calculated

Self-employment tax applies to 92.35% of your net self-employment profit, not the full amount, a long-standing feature of the formula (IRC Sec. 1402(a)) meant to roughly mirror how an employer's matching FICA contribution isn't itself treated as employee wages. That 92.35% figure is then taxed at 12.4% for Social Security, up to the annual wage base ($184,500 for 2026), plus 2.9% for Medicare, which has no cap at all.

If you also have W-2 wages from another job, those wages count first against the Social Security wage base. So if your W-2 wages already meet or exceed $184,500, none of your self-employment earnings owe the 12.4% Social Security portion, only the uncapped 2.9% Medicare portion.

Two Deductions That Offset It

Half of your self-employment tax is deductible above the line, reducing your adjusted gross income regardless of whether you itemize. On top of that, the Qualified Business Income (QBI) deduction, made permanent at 20% by the One Big Beautiful Bill Act, can shelter another chunk of your business profit, subject to a cap tied to your taxable income before the QBI deduction itself (and, at higher income for specified service businesses, additional phase-in limits this article doesn't model in full).

Additional Medicare Tax at Higher Income

Above $200,000 (single/head of household) or $250,000 (married filing jointly) of combined wages and self-employment earnings, an extra 0.9% Additional Medicare Tax applies on the excess. These thresholds are fixed by statute and don't get an annual inflation adjustment, unlike most other tax figures that move every year.

What Happens at Higher Income

Two things change once you earn enough. First, the 12.4% Social Security portion of SE tax stops once your combined wages and net SE earnings hit the annual wage base ($184,500 for 2026). The 2.9% Medicare portion keeps applying with no ceiling at all. Second, once combined wages and SE earnings cross $200,000 (single/head of household) or $250,000 (married filing jointly), an extra 0.9% Additional Medicare Tax applies on the amount above that threshold. A freelancer with $220,000 in net SE profit and $30,000 in outside W-2 wages, for example, has $203,170 in net SE earnings; combined with the W-2 wages that's $233,170, which is $33,170 over the $200,000 single threshold, adding roughly $299 of Additional Medicare Tax on top of everything else. The W-2 wages also eat into the Social Security wage base first, leaving only $154,500 of room for the SE earnings to be taxed at the 12.4% rate.

Sizing Your Quarterly Payments

The IRS generally expects payment as income is earned, not all at once in April; that's what quarterly estimated payments are for. For 2026, the due dates are April 15, June 15, September 15, and January 15, 2027. The safe harbor to avoid an underpayment penalty is paying, through withholding and estimated payments combined, at least 90% of the current year's tax or 100% of the prior year's tax (110% if your prior-year adjusted gross income was over $150,000). Because freelance income often varies month to month, it's worth recalculating the estimate whenever a quarter turns out meaningfully higher or lower than expected, rather than treating the first estimate as fixed for the whole year.

Who This Applies To

• Sole proprietors, freelancers, and independent contractors with $400 or more in net self-employment profit.
• Partners in a partnership who materially participate, on their share of partnership income.
• Anyone expecting to owe $1,000 or more in tax beyond what's already withheld generally needs to make quarterly payments.
• Anyone with a side freelance income on top of a regular W-2 job, since the two income streams interact through the shared Social Security wage base and Additional Medicare Tax thresholds shown above.

Common Mistakes

• Forgetting the 92.35% factor and calculating SE tax as a flat 15.3% of gross profit, which overstates the tax owed.
• Missing the half-SE-tax deduction when estimating income tax, which meaningfully lowers taxable income.
• Paying estimated tax based only on income tax and forgetting to include self-employment tax in the quarterly amount.
• Not accounting for outside W-2 wages when estimating the Social Security portion: wages from another job use up wage-base room first.

What This Doesn't Cover

The QBI deduction here is simplified. It doesn't model the phase-in range for specified service trades/businesses or W-2 wage/UBIA-of-property limits that apply at higher income, and this article doesn't calculate an exact underpayment penalty, only the safe-harbor targets to aim for. It also doesn't account for self-employed health insurance premiums or retirement plan contributions, both of which can further reduce taxable income beyond what's modeled here.