Excel stores dates as serial numbers counting days since January 1, 1900. This Excel Date calculator converts between Excel date serials and calendar dates. If you have ever seen a number like 45658 in a spreadsheet cell that should show a date, this tool is for you!
How Excel dates work
In Excel, January 1, 1900 is day 1, January 2, 1900 is day 2, and so on. This system makes date arithmetic simple: subtract two serial numbers to get days between them.
There is a quirk: Excel incorrectly treats 1900 as a leap year (it was not). This intentional bug was inherited from Lotus 1-2-3 for compatibility. Dates before March 1, 1900 are off by one day.
Excel vs. other systems
Google Sheets uses the same system. However, older Mac versions of Excel used January 1, 1904 as day 0 (the "1904 date system"). If dates seem off by about 4 years, check your workbook settings.
Related calculators
- Day Number Calculator - Days since Year 1
- Unix Day Calculator - Computing epoch
- Days Between Dates Calculator - Date subtraction
