The calculation, step by step

  1. Net profit. Income minus business expenses: the number self-employment taxes are computed on (Schedule C logic).
  2. Self-employment tax. 92.35% of net profit, taxed 12.4% for Social Security (up to the 2026 wage base) and 2.9% for Medicare, with the 0.9% Additional Medicare Tax above the statutory thresholds (Schedule SE). Below $400 of net earnings, no SE tax applies.
  3. Deductions. Half of SE tax, the 2026 standard deduction for your filing status, and the 20% Qualified Business Income deduction where it applies.
  4. Federal income tax. The 2026 marginal brackets for your filing status, applied to taxable income.
  5. Quarterly sizing. Total tax divided across the four estimated-tax deadlines, or the prior-year safe harbor (100% / 110% rule, IRS Pub 505) when that target is lawfully smaller.

Parameter values (wage base, standard deductions, brackets) come from the IRS revenue procedures for each year, including the 2025-law (OBBBA) revisions.

How we know it's right

The engine ships inside the Sero iPhone app as a Swift package with 19 worked-example tests, each an independently verified calculation locked against IRS-derived figures for 2025 and 2026. The calculator on this site is a separate TypeScript implementation, so we hold it to a harder standard: the Swift test suite exports 259 verification vectors(across both years, all four filing statuses, incomes from a loss to $300,000, W-2 interplay, and safe-harbor cases), and this site's test suite replays every one with exact equality. If web and app would ever disagree on a single dollar, the site fails to build.

What the estimate deliberately leaves out

Itemized deductions, tax credits, state brackets (a flat state rate is offered instead), local taxes, and multi-state situations. Modeling those poorly would be worse than saying plainly that we don't. For a complete picture, bring the export to a professional; Sero's job is the year-round habit, not the filing.

The honest frame

Sero gives you estimates to help you organize your finances and set money aside for taxes. Sero is not a tax preparer, accountant, or financial advisor, and nothing in the app is tax, legal, or financial advice. Estimates are based only on the information you enter and may not reflect your complete tax situation. Always confirm with a qualified professional before filing or making financial decisions. Sero does not file returns and does not move your money.

Run it yourself: the creator tax calculator.