Calculator methodology

Follow the calculation

Choose units first. Enter the values requested by the page, check any default rate or time period, and compare the result with the formula and example shown. Basic arithmetic is deterministic, but an estimate is only as useful as its assumptions.

Numbers and rounding

Tools use JavaScript numerical calculations. Most use floating-point numbers, which cannot represent every decimal exactly. Display precision differs between tools; use the stated rounding and avoid entering numbers outside the supported range. Keep full precision during a manual check and round the final answer.

Dates and time

Calendar dates, clock durations and elapsed time are different quantities. Read whether a tool includes the end date, allows overnight periods or uses a local date. Travel estimates use average speed; they do not model traffic, time-zone changes or daylight-saving transitions.

Money and rates

Use one currency consistently. A currency symbol is a label, not an exchange-rate conversion. Loan estimates assume the stated payment frequency and fixed rate. Actual fees, tax, insurance and lender rounding can change payments.

Checks completed

During the October 2026 updates we ran targeted calculation checks for selected tools, including scientific expressions, fractions, bill splitting, interest, dates, fuel cost, download estimates, travel time and price comparisons. This is a record of targeted checks, not a certification of every calculator or every input.

Report a discrepancy

Use feedback to share the page address, non-sensitive inputs, expected result and actual result. Do not send account numbers or private financial or health records.

Updated 9 October 2026. Editorial policy.