How Excelavon’s tools calculate their answers, how they are checked, and where the information in guides comes from.
Sources
- Microsoft Support: Excel functions (alphabetical and by category). The reference for what each function does, its arguments, and which versions include it.
- Microsoft Support: date systems in Excel. The 1900 and 1904 date systems and the 1900 leap-year compatibility rule used by the date serial converter.
- HyperFormula (open-source spreadsheet calculation engine, GPLv3). Used only to cross-check the formulas our tools generate; it is not part of the pages you load.
Method
- All tools run in your browser. Nothing you type is sent to our server.
- Each tool’s calculation is tested against fixed worked examples with known answers, for example a 200,000 loan at 6% over 30 years (1,199.10 a month), 1 January 2023 as serial 44927, column XFD as 16,384, and 15 January 2020 to 20 March 2023 as 1,160 days (3 years, 2 months, 5 days).
- The formulas the tools print, such as DATEDIF, NETWORKDAYS, PMT, VLOOKUP, XLOOKUP and INDEX/MATCH, are evaluated in HyperFormula on the same examples, and the result must match the tool’s own answer.
- Inputs outside the range Excel supports (dates before 1900 or after 9999, columns past XFD) return a message rather than a number.
Corrections are listed on the corrections page. The rules for guides are in the editorial policy.