Self-employment tax is universally quoted as 15.3%. The effective rate on your net profit is 14.13%.
On $100,000 of profit that is $14,130, not $15,300 — a $1,170 difference produced by a statutory factor most people have never heard of, and it recurs at every income level.
And it stops. The Social Security portion caps out at $199,783 of net profit for 2026, above which your marginal self-employment tax rate falls from 15.3% to 2.9%. Someone earning $250,000 pays an effective 11.94%.
By the end of this guide you will know exactly what you owe and when, what rate you must charge to match a salaried job, how to reserve so April is uneventful, how to use the safe harbour so an underpayment penalty becomes impossible, and how to judge whether an S-corp election is worth its costs for your numbers.
A note before you start. This is general education, not personalised tax, legal or financial advice. Federal figures are for tax year 2026: the Social Security wage base of $184,500 comes from the Social Security Administration, and bracket and standard deduction figures from IRS Revenue Procedure 2025-32. Computations are performed by this site's own tax engine on a single filer taking the standard deduction with no dependents unless stated. No state or local tax is included in any self-employment figure here — states tax business income differently and twelve permit a local income tax on top. Anyone with real self-employment income should be working with a licensed tax professional; this guide exists to make you a better-informed client, not to replace one. This site takes no lead-generation and no affiliate money.
Why 15.3% is not the rate you pay
Self-employment tax is the self-employed equivalent of FICA. An employee pays 7.65% and their employer pays another 7.65%; you pay both halves, which is where 15.3% comes from.
But it is not charged on your whole profit. Under 26 U.S.C. § 1402(a)(12), only 92.35% of net earnings is subject to it — the statute's way of approximating the deduction an employer gets for its own share.
So on $100,000 of profit:
| Net profit | $100,000 |
| × 92.35% | $92,350 — the amount actually taxed |
| Social Security at 12.4% | $11,451 |
| Medicare at 2.9% | $2,678 |
| Total SE tax | $14,130 |
| Effective rate on profit | 14.13% |
That 14.13% holds at every level until the wage base, which is what makes it worth memorising:
| Net profit | SE tax | Effective rate |
|---|---|---|
| $30,000 | $4,239 | 14.13% |
| $50,000 | $7,065 | 14.13% |
| $75,000 | $10,597 | 14.13% |
| $100,000 | $14,130 | 14.13% |
| $150,000 | $21,194 | 14.13% |
| $200,000 | $28,234 | 14.12% |
| $250,000 | $29,851 | 11.94% |
Look at the last two rows. Between $200,000 and $250,000 of profit — $50,000 more — the SE tax rises by only $1,617. That is the wage base at work.
The crossover, and why it matters for planning
The Social Security portion applies only up to the wage base, $184,500 for 2026. Because only 92.35% of profit counts, you reach that ceiling at:
$184,500 ÷ 0.9235 = $199,783 of net profit.
Below it, your marginal SE rate is 15.3%. Above it, 2.9% — just the Medicare portion, which has no cap.
Two planning consequences follow immediately.
A dollar of profit above $199,783 is far cheaper in SE tax than a dollar below it. If you have discretion about timing — deferring an invoice, accelerating an expense — the year in which profit lands changes what it costs.
And an S-corp election is worth much less above the crossover than below it, because the SE tax you would be avoiding is already down to 2.9%. Section 11 covers this properly, and it is the reason S-corp advice aimed at $80,000 businesses does not transfer to $300,000 ones.
And the mistake that costs more than any of this
Every figure above is arithmetic. The expensive failure is not arithmetic — it is that nothing was withheld and nobody moved the money.
An employee never sees their tax. It is deducted before the payment lands, and the number in their account is theirs to spend. A self-employed person receives the gross, every time, and a portion of it is already owed to someone who will ask for it later.
The gap between those two facts is where solvent businesses fail. Not because the business was unprofitable — because a year's tax was quietly spent as it arrived, and the bill came in one piece.
The fix is mechanical and takes an afternoon. A separate account, a fixed percentage moved on the day each payment clears, quarterly instalments paid from that account and nowhere else. Section 2 sets the percentage and the mechanism, and it is the most valuable page in this guide — more valuable than the S-corp analysis, more valuable than the deduction list, because it is the one that determines whether any of the rest ever becomes a problem.
Everything after this line is the operating manual: what you owe and in what order, the reserve percentage, the rate you must charge, the safe harbour that makes an underpayment penalty impossible, what to do when profit swings mid-year, the deductions worth getting right, a worked year end to end, retirement accounts that do far more here than for an employee, the structure question, when an S-corp actually pays for itself, and the state layer none of these federal figures include.