Excel Serial Number Converter

Excel stores a date as a number: the count of days since 1900-01-01, which is serial 1. When a cell is formatted as General or Number rather than Date, that raw number is what you see. It shows up most often right after importing a CSV, or after pasting a date column into another system.

1900 was not a leap year, but Excel counts 1900-02-29 as if it existed, for compatibility with an older spreadsheet. Serial 60 therefore points at a date that never happened, and serials from 61 onwards line up if you count days from 1899-12-30. This tool splits the two ranges accordingly.

Early Mac versions of Excel counted from 1904-01-01. The setting still exists, and copying dates between workbooks that disagree shifts them by 1,462 days. Switch the buttons above if that matches what you are seeing.

The fraction of a serial number is the share of a 24 hour day. 0.25 is 06:00:00 and 0.5 is 12:00:00. The tool appends a time only when a fraction is present.

In the 1900 system it is 2023-03-15. Pasting 45000 into this tool gives the same answer. In the 1904 system it is 2027-03-16.

Excel treats 1900 as a leap year, which it was not, so serial 60 points at 1900-02-29. That date does not exist, so the tool reports it instead of inventing a value.

Yes. The integer part is the date and the fraction is the share of a 24 hour day. 0.5 is 12:00:00, and the time is shown whenever a fraction is present.

No. Detection and conversion happen entirely inside your browser. Nothing you enter leaves the page.