Methodology

This page explains the standard every calculator on Allcalcy is held to. Each individual tool also names the specific formula and authority it relies on.

Verified formulas

Formulas come from named, authoritative sources rather than being reinvented. Each one is checked against independently calculated worked examples before it ships, and those examples are encoded as automated tests so a future change cannot silently break a result.

Rounding and money

Amounts of money are computed in whole cents and rounded half up at the point of display. For schedules such as a loan amortization, the final payment is adjusted so the balance closes to exactly zero and the parts add back up to the original amount. This mirrors how real lenders handle the last installment.

Dates and units

Dates use real calendar arithmetic, never an approximate average year length, so ages and durations are exact. Unit conversions use exact factors. Temperature is converted with the correct affine formulas rather than a simple ratio.

Currencies and regions

For most tools a currency is a display choice only; the underlying math is identical whatever symbol you pick. Tools that depend on real rules, such as income tax, switch the actual rates and brackets by region rather than only changing the symbol.

Testing

The calculation core is covered by unit tests, golden worked examples, and property tests that check invariants hold across thousands of random inputs. A failing math test blocks a release.

Limitations

A calculator is a model, not a guarantee. Results depend on the figures and assumptions you provide and cannot account for every personal circumstance. Treat them as well-grounded estimates and verify anything important with a qualified professional.