Methodology: How We Calculate Your Taxes

This page documents exactly where every figure in US Tax Calculator comes from and how each calculation is performed, so you can verify our work against the primary sources yourself.

Federal Income Tax Brackets & Standard Deduction

2026 federal tax brackets, the standard deduction amounts, and related inflation-adjusted thresholds are taken from IRS Revenue Procedure 2025-32. 2025 figures use the prior year's official Rev. Proc.; 2027 figures are our own projected estimates (inflation-indexed forward from 2026), explicitly labeled as projections, not official IRS numbers.

Tax is computed using the standard progressive-bracket method: each dollar of taxable income is taxed at the rate for the bracket it falls into, not at a single flat rate applied to the whole amount.

FICA / Payroll Tax

Social Security tax is 6.2% on wages up to the annual wage base ($184,500 for 2026), set each year by the Social Security Administration. Medicare tax is 1.45% with no wage cap, plus the 0.9% Additional Medicare Tax above $200,000 (Single) / $250,000 (Married Filing Jointly).

Self-Employment Tax

Follows IRC §1401: 92.35% of net self-employment earnings is subject to 12.4% Social Security (up to the same wage base) plus 2.9% Medicare, and 50% of the resulting SE tax is an above-the-line deduction.

Long-Term Capital Gains

Taxed at 0% / 15% / 20% preferential rates based on Rev. Proc. 2025-32 thresholds, stacked on top of ordinary income. We do not model the 3.8% Net Investment Income Tax (NIIT).

Child Tax Credit

Amount, refundable portion, and phase-out thresholds follow current-law 2026 figures including OBBBA adjustments.

State Income Tax

All 50 states plus DC use each state's own published tax-department bracket tables, flat-rate figures, or "no income tax" status, applied on each state's own rules rather than assuming federal conformity.

What This Calculator Intentionally Does Not Model

• Alternative Minimum Tax (AMT)
• 3.8% Net Investment Income Tax (NIIT)
• Earned Income Tax Credit (EITC) and other income-based refundable credits
• Education credits (AOTC, Lifetime Learning Credit)
• Local (city/county) income taxes
• Prior-year carryovers (capital loss carryforwards, etc.)

Review Cadence

We review every calculator against the latest IRS and SSA guidance at least once per tax year, and immediately whenever the IRS issues a mid-year correction. Last reviewed July 2026.

Corrections

Found a figure that doesn't match the official source? Email [email protected] with the page, the number in question, and a link to the IRS/SSA source you're comparing against.