How we verify

Every calculator page goes through the same checks before it ships.

First, the formula is matched to at least two outside sources, such as an official guideline, a standards body, or a well kept reference. Second, one full example is worked by hand and then run through the page tool to confirm the same result. Third, edge cases are tried: zeros, very large inputs, and crossed unit systems.

Limits are stated on the page. Health tools give estimates for information only. Money tools leave out taxes and fees unless the page says otherwise. When a mistake is reported, the page is fixed and the correction is noted.