Time & automation / Spreadsheets
Excel Date Converter: Serial Numbers to Dates and Back
Convert Excel date serial numbers such as 45000 to dates and times, and dates back to serial numbers, in batches, in both the 1900 date system used by Windows Excel and the 1904 system from old Mac files, with the fictional 29 February 1900 flagged.
Excel Date Converter: Serial Numbers to Dates and Back: Excel counts days from a starting point and stores the time as a fraction of a day: in the 1900 system, 45000 is 15 March 2023 and 45000.75 is 18:00 that day. Serial 60 is 29 February 1900, a date that never existed, so dates before it are one serial earlier than a plain day count. In the 1904 system the same day is 43538, 1,462 lower. Runs 100% locally in your browser with zero server file uploads.
- Category
- Developer tools
- Runs
- In your browser
- Cost
- Free · no sign-up
- Availability
- Ready to use
Runs entirely in your browser
| Serial | Date and time |
|---|---|
| 45000 | 2023-03-15 |
| 45000.75 | 2023-03-15 18:00 |
| 60 | 29 February 1900, which never existed |
| 1 | 1900-01-01 |
| Date | Serial |
|---|---|
| 2023-03-15 | 45000 |
| 2023-03-15 18:00 | 45000.75 |
| 2000-01-01 | 36526 |
Excel stores dates as the number of days since a starting point, with the time of day as a fraction: 45000.75 is 15 March 2023 at 18:00. In the 1900 system, used by Windows Excel, 1 is 1 January 1900, and serial 60 is 29 February 1900, a day that never existed: Lotus 1-2-3 treated 1900 as a leap year, and Excel copied it for compatibility. The 1904 system, from early Mac versions, starts at 0 on 1 January 1904, 1,462 days later. Times have no time zone.
Checked against openpyxl
The conversions match openpyxl's from_excel and to_excel, including the jump at serial 61, 1 March 1900, and the 1904 epoch.
Other timestamps
To convert Unix timestamps in seconds or milliseconds, use the Unix timestamp converter.
How to use it
- Choose the 1900 or 1904 date system.
- Paste serial numbers or dates, one per line.
- Read the converted values in the tables.
Privacy & limitations
Everything is converted in your browser.
Related tools
Frequently asked questions
Why does my CSV show 45000 instead of a date?
The spreadsheet stored the date as its serial number and the export lost the date format; convert it here or format the column as a date.
Why is 1900 treated as a leap year?
Lotus 1-2-3 had the bug, and Excel copied it so that spreadsheets would give the same results; Microsoft kept it for compatibility.
When is the 1904 system used?
In workbooks created by old Mac versions of Excel, or where the option is turned on; mixing the two systems shifts dates by four years and a day.
Free tool · runs in your browser · no account required