How We Calculate

Transparency matters, so this page explains the methods behind our tools.

Loan calculators

Mortgage, auto, personal and student loan results use the standard amortization formula M = P * r / (1 - (1 + r)^-n), where P is the amount financed, r the monthly interest rate (APR divided by 12) and n the number of monthly payments.

Savings and retirement

Future value adds compound growth on a starting balance to the growth of regular monthly deposits. Returns are assumptions you enter, not forecasts. The retirement tool also shows the common 4% withdrawal guideline.

Tax and paycheck

Federal tax uses 2025 US marginal brackets and the standard deduction for single and married filing jointly. Payroll tax is 7.65% (Social Security and Medicare). State tax is a flat percentage you set. Credits, itemized deductions, pre-tax benefits and local taxes are not included.

Insurance cost estimators

No calculator can know your insurer's private pricing. Our insurance tools combine a base cost with multipliers for the main rating factors (age, value, location, coverage level) calibrated to broad market averages. They are meant for budgeting and comparison, not as quotes.

Health calculators

BMI follows the CDC adult formula and categories. Calorie needs use the Mifflin-St Jeor equation with standard activity multipliers. These are screening estimates and not medical advice.

Updates

We review tax brackets and assumptions each year and whenever a reader reports an issue. Last review: October 2026.