Formula selection
Each calculator states its formula beside the interactive result. We use standard mathematical definitions, fixed unit relationships, and conventional fixed-rate amortization methods. Worked examples make the inputs, substitutions, and expected output inspectable without relying on hidden server logic.
Reference standards
Where an external standard or public authority is relevant, the calculator page links directly to that source. Core references currently include:
- CDC — Calculating BMI
- Consumer Financial Protection Bureau — How mortgage amortization works
- Investor.gov — Compound Interest Calculator
- NIST Guide to the SI — Conversion Factors
Precision and rounding
Calculations retain full available numeric precision internally and round values for readable display. A displayed result can therefore differ slightly from a value rounded at every intermediate step. Unit converters identify important distinctions such as US liquid gallons versus imperial gallons.
Validation and testing
The shared calculation engine is tested with normal inputs as well as empty, invalid, zero, negative, decimal, boundary, and overflow cases. Calculator-specific constraints reject impossible physical values while preserving mathematically meaningful negative or zero values where appropriate.
Limits of the results
Finance results are educational estimates and do not include every fee, tax, insurance cost, lender rule, or investment risk. Health results are screening information, not medical advice or diagnosis. Important decisions should be checked independently with a qualified professional.
Corrections
If a formula, source, unit, label, or edge case appears incorrect, use the contact page and include the calculator URL, inputs, observed result, and expected result. Reproducible reports are reviewed against the displayed formula and test coverage.