Every result should be explainable.

Calculation principles

1. Show the formula. Each calculator states how the output is produced.
2. Keep inputs editable. Defaults are examples, not claims about a user or location.
3. Separate arithmetic from rules. A fee total can be calculated without claiming the fee is permitted.
4. Expose uncertainty. When multiple methods are common, we show a comparison or let the user choose.
5. Test edge cases. Calculations should handle zero, missing, decimal, and unusually large inputs without breaking.

Privacy boundary

Calculations run in the browser. Analytics may record the calculator name and whether a calculation was completed, but not the rent, salary, deposit, dates, lease text, address, or other raw values entered.

Review and corrections

Each tool shows a last-reviewed date. Material corrections update the formula or explanation and the review date.