Self-Employment Tax Explained (the 15.3%)
Where the 15.3% comes from, why only 92.35% of your profit counts, and why you get to deduct half.
If you freelance, run a side business, drive for a rideshare app, or operate as a single-member LLC, you have probably bumped into a tax that traditional employees never see on their pay stub: self-employment (SE) tax. It often surprises new business owners because it lands on top of regular income tax, and it can be the single largest line on a small-business return.
The good news is that self-employment tax is mechanical and predictable once you understand its parts. This guide walks through the 15.3% headline rate, the 92.35% adjustment, the Social Security wage cap, the extra Medicare tax for high earners, and the deduction that softens the blow.
What self-employment tax actually pays for
When you work for an employer, your paycheck has Social Security and Medicare taxes withheld. These are sometimes labeled "FICA." Your employer pays a matching amount behind the scenes, so the total contribution is split between the two of you.
When you are self-employed, there is no employer to split with. You are effectively both the employer and the employee, so you owe both halves yourself. That combined obligation is what we call self-employment tax. It is not a separate "extra" tax on entrepreneurs; it is the same Social Security and Medicare system, just collected differently.
Breaking down the 15.3%
The 15.3% rate is really two taxes bundled together:
- 12.4% for Social Security (6.2% employee share + 6.2% employer share)
- 2.9% for Medicare (1.45% employee share + 1.45% employer share)
Add them up and you get 15.3%. These percentages have been stable for many years, but tax law can change, so always confirm the current rates on IRS.gov before filing.
Why only 92.35% of your profit is taxed
Here is the part that trips people up. You do not multiply 15.3% by your full net business profit. First you multiply your net earnings by 92.35% (which is 100% minus 7.65%).
Why 92.35%? Because employees do not pay Social Security and Medicare tax on the employer's half of FICA. To keep the self-employed on roughly equal footing, the rules let you remove an amount that mirrors that employer share before applying the SE tax rate. The result is a smaller taxable base.
Example: Suppose your business nets $50,000 in profit for the year. First, multiply by 92.35%: $50,000 × 0.9235 = $46,175. That $46,175 is your SE-taxable earnings. Then apply 15.3%: $46,175 × 0.153 ≈ $7,065. That is your self-employment tax for the year (assuming you are below the Social Security wage cap, discussed next).
The Social Security wage base cap
The 12.4% Social Security portion only applies up to an annual limit called the wage base. Once your combined wages and SE earnings reach that ceiling, you stop owing the Social Security piece for the rest of the year. The wage base changes every year, so we will not print a specific dollar figure here that could quickly go stale. You can find the current number at SSA.gov or in the SE tax instructions on IRS.gov.
One important wrinkle: if you also have a W-2 job, the Social Security taxes already withheld from that paycheck count toward the cap. Your SE tax calculation accounts for those wages so you are not taxed twice on the same Social Security ceiling.
Medicare has no cap (plus a 0.9% surtax)
Unlike Social Security, the 2.9% Medicare portion has no income ceiling. It applies to every dollar of your SE-taxable earnings, no matter how high your income climbs.
On top of that, high earners owe an Additional Medicare Tax of 0.9% on earnings above a threshold set by filing status (for example, the threshold for a single filer differs from a married-filing-jointly couple). This surtax is the employee-only portion; there is no employer match to mirror, so it is not doubled. If your income is in that range, check the current thresholds on IRS.gov, since they are not indexed for inflation and rarely change.
The deduction for half of your SE tax
Self-employment tax has a built-in consolation prize. You can deduct one-half of your SE tax as an above-the-line adjustment to income. "Above-the-line" means you get the deduction whether or not you itemize, and it reduces your adjusted gross income.
Continuing the earlier example: if your SE tax is about $7,065, you can deduct roughly $3,533 against your income tax. This does not reduce the SE tax itself, but it lowers the regular income tax you owe. It reflects the idea that an employer would normally deduct its share of payroll taxes as a business expense.
- The deduction reduces income tax, not self-employment tax.
- It is available even if you take the standard deduction.
- You still owe the full SE tax; only your income-tax base shrinks.
How this connects to quarterly estimated taxes
Because no employer withholds taxes from your business income, the IRS generally expects you to pay as you go through quarterly estimated taxes. Those payments need to cover both your income tax and your self-employment tax. Underpaying during the year can trigger penalties, even if you settle up by the filing deadline.
A practical habit is to set aside a percentage of every payment you receive into a separate savings account so the money is ready when estimates are due. To get a rough sense of what to send each quarter, try our calculator, which can help you ballpark the combined income and SE tax burden. Treat the result as a planning estimate, not an exact filing figure.
Frequently Asked Questions
Do I owe self-employment tax if my business lost money?
No. SE tax applies to net earnings. If your business had a loss or very small profit (generally below a small annual threshold), you typically owe no SE tax for that activity. Verify the current minimum on IRS.gov.
I have a W-2 job and a side gig. Do I pay SE tax twice on Social Security?
No. The Social Security wage base is a combined ceiling. Wages already taxed at your W-2 job count toward the cap, so your SE tax calculation reduces the Social Security portion accordingly. Medicare still applies to all earnings.
Is self-employment tax the same as income tax?
No. They are separate. SE tax funds Social Security and Medicare, while income tax is calculated on your taxable income using ordinary tax brackets. Most self-employed people owe both, which is why total tax bills can feel high.
Can forming an S corporation reduce SE tax?
Sometimes, because an S corporation owner can split earnings into "reasonable salary" (subject to payroll taxes) and distributions (generally not subject to SE tax). This strategy has rules, costs, and IRS scrutiny, so discuss it with a licensed tax professional before acting.
This article is educational only and not financial, tax, or legal advice. MoneyPencil is not a lender, tax preparer, insurer, or financial advisor. Tax rates, wage bases, and thresholds change; verify current figures with IRS.gov, SSA.gov, and a licensed professional before making decisions.