Methodology

Paycheck calculator

The paycheck calculator estimates annual tax liability and divides it evenly across pay periods. It is closest to what an employer withholds when your W-4 is simple and your income is steady.

1. Gross pay is annualized: salary as entered, or hourly wage × hours per week × 52, or per-period pay × the number of periods (12, 24, 26, or 52).
2. Pre-tax deductions are removed: 401(k)/403(b) contributions (capped at the 2026 limit of $24,500) and Section 125 health, HSA, and FSA amounts. Health-type deductions are also excluded from Social Security and Medicare wages; retirement contributions are not.
3. Federal income tax: taxable income = gross − pre-tax deductions − the standard deduction for your filing status ($16,100 / $32,200 / $24,150 for 2026). The seven marginal brackets are applied. No credits or itemized deductions.
4. Social Security: 6.2% of FICA wages up to $184,500. Medicare: 1.45% of all FICA wages plus 0.9% above $200,000 (single) or $250,000 (joint).
5. State income tax: gross − pre-tax deductions − the state's standard deduction − personal and dependent exemptions (or, where the state structures the exemption as a credit, the credit is subtracted from tax). Brackets are applied using the single or married-filing-jointly schedule; head of household uses the single schedule unless the state publishes its own. Where a state phases out its exemption by income, the phase-out is modeled using gross wages as a proxy for adjusted gross income.
6. Local income tax is included only where selected: all Maryland counties, New York City, Yonkers (approximated), and Philadelphia. Other local taxes are noted on the state page but not calculated.
7. State payroll programs (disability, paid family and medical leave, long-term care) are applied at the employee rate up to any wage cap.

Not modeled: tax credits, itemized deductions, W-4 adjustments other than extra withholding, bonuses and supplemental wage rates, garnishments, nonresident and multi-state situations, and state rules noted in the "What this estimate leaves out" list on each state page.

Mortgage calculator

Principal and interest use the standard amortization formula P × r(1+r)ⁿ ÷ ((1+r)ⁿ − 1). Property tax is the home price × the annual rate ÷ 12. Insurance and HOA are divided by 12. PMI is the annual PMI rate × the current balance ÷ 12 and stops once the balance falls to 80% of the purchase price. Extra payments are applied to principal each month and the schedule is re-run to compute interest and time saved.

Defaults per state: the property tax rate is the statewide effective rate on owner-occupied housing from the Tax Foundation's analysis of Census Bureau American Community Survey data; the home price is Zillow's Home Value Index for the state; the interest rate is Freddie Mac's latest weekly national average (30- or 15-year). Homeowners insurance defaults to 0.35% of the home price per year, a national rule of thumb, and should be replaced with a quote. All defaults are editable.

Sales tax calculator

Tax = price × combined rate. The reverse calculation is price = total ÷ (1 + rate). State rates and population-weighted average local rates come from the Tax Foundation's midyear compilation of state revenue department and Sales Tax Clearinghouse data. "Highest combined rate" uses the maximum local rate reported for the state. Grocery treatment is summarized from state law; product-specific rules (clothing, vehicles, prepared food) vary and are only noted.

Loan payoff calculator

Each month, interest = balance × APR ÷ 12; the payment (plus any extra) less interest reduces the balance. A lump sum is applied before the first month. If the payment does not exceed the first month's interest, the loan is flagged as never paying off. If no payment is entered, one is computed from the remaining term using the amortization formula.

Compound interest calculator

The nominal rate and compounding frequency are converted to an effective annual yield, (1 + r/n)ⁿ − 1, then to an equivalent monthly factor. The balance grows each month and the contribution is added at month end. Contributions can rise by a fixed percentage each year. "Today's dollars" divides each year's balance by (1 + inflation)^years.

Retirement calculator

Each year: employee contribution = salary × your percentage; employer match = salary × min(your percentage, match cap) × match rate. The combined amount is added monthly while the balance grows at the assumed return converted to a monthly rate. Salary grows annually by the raise percentage. The target nest egg is desired income ÷ withdrawal rate in today's dollars, inflated to the retirement year for comparison. Taxes on withdrawals, Social Security, pensions, and market volatility are not modeled.

Rounding and display

Calculations run at full floating-point precision and are rounded to the cent only for display. Percentages are shown to two or three decimals as the source publishes them. Annual figures divided across pay periods can differ from a real pay stub by a few cents because of how payroll systems round each period.

Testing

Every engine has an automated test suite that checks results against published worked examples (for instance, the IRS federal tax on a $75,000 single filer, the textbook payment on a $300,000 loan at 6%, and the West Virginia Tax Division's 2026 rate table). Data files are validated for structure and internal consistency (ascending brackets, plausible ranges, complete coverage of all 51 jurisdictions) on every build.