How Our Tax Calculators Work

The Calculation Methodology

Every calculator on this site uses the official formulas published by the Internal Revenue Service in Schedule SE instructions and the state tax brackets published by each state's Department of Revenue. We do not use approximations — each calculation follows the exact same steps a tax professional would use.

Self-employment tax calculation: Your net profit (gross income minus business expenses) is multiplied by 92.35% to determine net earnings subject to SE tax. The 15.3% rate is applied (12.4% Social Security on the first $184,500 in 2026, plus 2.9% Medicare on all earnings). An additional 0.9% Medicare surtax applies above $200,000 for single filers.

Income tax calculation: We subtract the 50% SE tax deduction, standard deduction ($16,100 single / $32,200 married in 2026), and Qualified Business Income deduction (20% of QBI, with phase-outs starting at $201,775) from your adjusted gross income. The resulting taxable income is taxed progressively through the seven federal brackets (10% to 37%) and your state's brackets.

Quarterly estimates: We calculate your projected annual tax and apply IRS safe harbor rules — the lesser of 90% of current-year tax or 100% of prior-year tax (110% if AGI exceeds $150,000) — divided into four equal quarterly payments.

Data Sources

Federal tax data comes from IRS Revenue Procedure 2025-32 and IR-2025-103 (inflation adjustments for tax year 2026). State tax data comes from each state's Department of Revenue publications and the Tax Foundation's annual state tax survey, cross-verified against official state sources.

Tax data refreshes automatically via our data pipeline. When the IRS or a state changes rates, brackets, or deductions, our calculators update within 24 hours.

Accuracy & Limitations

Our calculators are designed for estimates, not filing. They account for: self-employment tax, federal income tax, state income tax, the QBI deduction, standard deduction, and safe harbor quarterly estimates. They do not account for: itemized deductions, tax credits (EITC, child tax credit), capital losses, AMT, or unusual tax situations.

Your actual tax liability depends on your complete financial picture. Always verify results with official IRS forms or a qualified tax professional before filing.