Visible formulas
Each calculator explains its formula, assumptions and an example. Inputs are checked before calculating. Invalid or non-finite results are not presented as usable answers.
Precision and conventions
Results display up to 8 decimal places. Calculations use the unrounded values; very small values use scientific notation. JavaScript floating-point arithmetic can introduce tiny rounding differences.
Date tools use calendar dates and explicit leap-day conventions. Unit tools identify variants such as US liquid gallons and mechanical horsepower. NIST publishes the SI conversion reference.
Scope
This edition contains 208 calculators. Country tools use their own currency, assumptions and scope. Published government sources are linked where specific rules apply. Illustrations are not bank offers or guarantees.
US planning conventions
Mortgage results separate principal and interest from property taxes, insurance, PMI and HOA dues. Annual costs are converted to monthly amounts only where the input labels state that convention. Auto-loan fees and sales tax enter through their named fields.
Hourly pay conversion produces gross income, before withholding and benefits. Debt-to-income uses recurring monthly obligations divided by gross monthly income. Neither ratio nor projected payment establishes loan approval.