Dates & time
Excel date serial converter
Translate date-times and spreadsheet serials while exposing the 1900 leap-day anomaly.
A clear answer. Here’s how.
Uses spreadsheet wall-clock arithmetic, with the fractional part representing a 24-hour day. In the 1900 system, 1900-01-01 is 1 and the fictitious serial day 60 is rejected; in 1904, 1904-01-01 is 0. The 1900 system supports actual dates from 1900-01-01 onward, while the 1904 system supports dates from 1904-01-01. Reverse output rounds to milliseconds. No time zone or spreadsheet locale is inferred.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Direction
- Calendar → serial
- Workbook date system
- 1900 date system
- Calendar date-time (YYYY-MM-DDTHH:MM:SS)
- 2011-07-05T00:00:00
Example result
- Calendar wall date-time
- 2011-07-05T00:00:00.000
- Spreadsheet serial
- 40,729
- Workbook date system
- 1900
Wall-clock value without a time zone. Serial 60 in the 1900 system is intentionally rejected.