Self-Employment Tax Calculator

If you or your spouse also has a W-2 job

A side business on top of a day job is easy to estimate wrong. Your wages fill the Social Security limit first, so a high enough salary means the 12.4% portion never touches your side profit and only the Medicare share is left. The limit is per person: your spouse's wages never use up your room, and when you are both self-employed, each business gets its own calculation. Enter each person's numbers separately and the calculator applies the right limit to each of you.

Quarterly payments and the safe harbor

Nobody withholds anything for you when you work for yourself, and the IRS wants its money during the year, so the system runs on four estimated payments. For 2026 they are due:

You don't have to predict the year perfectly. The penalty rules are satisfied once your payments reach the smaller of 90% of this year's tax or 100% of last year's total tax, and 110% of last year's once your prior AGI passes $150,000 ($75,000 married filing separately). That is why the calculator asks about last year's return: with those two lines it can show the smallest payment that keeps you penalty-free instead of a guess. If you fall short, the penalty is figured like interest on the shortfall, quarter by quarter, so catching up later in the year stops more penalty from building, even though it doesn't erase what already accrued.

What if I pay too much, or not enough?

Federal tax is pay-as-you-earn. It is due as the money is earned rather than in one bill the following April, and with no employer withholding for you, four payments a year is how that happens.

Come up short in a quarter and the penalty is figured separately for each payment period, so sending everything in April does not undo a shortfall from June. The part that surprises people: you can be charged that penalty in a year you still get a refund, because the two are measured differently. Reaching the safe-harbor amount by each due date is what avoids it.

If your income lands unevenly, a trade that earns most of its money in summer or a year with one large project, the annualized income installment method (Schedule AI on Form 2210) lines your required payments up with the quarters the income actually arrived in. It often reduces or removes a penalty that the flat four-way split would have caused.

Pay in more than you owe and the extra comes back as a refund when you file, or you can leave it with the IRS as a credit toward next year's first payment. Worth knowing before you choose the credit: once an overpayment is applied that way, you cannot have it refunded until you file the following year's return.

What this estimate includes, and what it leaves out

This calculator runs the federal return's order of operations: self-employment tax per person, the extra 0.9% Medicare tax at higher incomes, the deduction for half of SE tax, the taxable share of Social Security benefits, the standard deduction with the extra amounts at 65 and older, the senior deduction, the QBI deduction (without the high-income service-business limits), the regular brackets, and the lower capital-gains rates on long-term gains and qualified dividends.

The biggest thing it skips is tax credits, and the child tax credit alone changes the answer for many families. Itemizing and state returns are outside it too. Treat the result as a planning number, and have the actual return prepared from your real records.