Methodology and sources

This page explains where the figures behind the calculators come from, how they are used and what they do not cover. Data was last reviewed on October 4, 2026.

Federal income tax (2026)

Brackets and standard deductions for single, married filing jointly and head of household filers come from IRS Revenue Procedure 2025-32. The standard deduction used is $16,100, $32,200 and $24,150 respectively. Tax is computed marginally, bracket by bracket.

Social Security and Medicare

Social Security is 6.2% of wages up to the 2026 wage base of $184,500, published by the Social Security Administration. Medicare is 1.45% of all wages, plus 0.9% on wages above $200,000 ($250,000 for joint filers). Both are applied to gross pay.

State income tax

Each state's brackets, standard deduction, personal exemption and personal credit come from Tax Foundation, State Individual Income Tax Rates and Brackets, 2026. State tax is computed as:

1. Gross pay minus pre-tax deductions.
2. Minus the state standard deduction and personal exemption.
3. Taxed through the state's brackets.
4. Minus any personal credit, never below zero.

Known simplifications:

• State tables are published for single and joint filers. Head of household uses the single table.
• Local income taxes are not included.
• Deduction, exemption and credit phase-outs at higher incomes are not modeled.
• Dependents are not included.
• For states that index brackets to inflation and had not published 2026 thresholds at the time of the source table, the prior year's thresholds are used. The state page says so where this applies.

Sales tax

State and average local sales tax rates as of January 1, 2026 come from Tax Foundation, State and Local Sales Tax Rates, 2026. The combined rate is the state rate plus the population-weighted average local rate. Your exact local rate may differ.

Loans

Mortgage, auto loan and credit card calculations use standard fixed-rate amortization with monthly compounding. Mortgage PMI is estimated at 0.75% of the loan amount per year when the down payment is under 20%; real quotes vary by lender, credit score and loan type.

Savings

The compound interest calculator compounds monthly, adds contributions at the end of each month and assumes a constant rate of return. Real returns vary from year to year.

Calories

The TDEE calculator uses the Mifflin-St Jeor equation for basal metabolic rate and standard activity multipliers. It is a population estimate, not a measurement, and is not medical advice.

Testing

Each calculator's math is covered by automated tests that compare results with values worked out by hand from the published tables. The worked examples on each page are generated from the same code the calculator runs, so the text and the tool always agree.

Updates and corrections

Tax figures are reviewed when the IRS, the Social Security Administration and state sources publish new annual amounts. If you spot an error, please contact us.