Excel Date Converter
Convert Excel serial date numbers to readable dates
About the Excel Date Converter
Dates in Excel and Google Sheets are stored internally as plain numbers called serial values. January 1, 1900 is 1 in Excel, January 2 is 2, and the counter has been incrementing ever since — so a modern date like June 29, 2026 is stored as 46201. When you format a cell as a date, the spreadsheet simply translates that integer into a readable string. When you format it as a number, the mask comes off and you see the serial value underneath.
There is a well-known quirk: Excel's 1900 date system incorrectly treats February 29, 1900 as a real date (it was not a leap year), adding a phantom day that shifts all dates after February 28, 1900 up by one. Google Sheets uses the same 1900 system by default and carries the same bug. Older Macintosh Excel workbooks use a 1904 date system that starts counting from January 1, 1904. This tool converts in both directions — serial number to date and date to serial number — for both systems, with the leap-year bug accounted for in the 1900 calculation.
How to Use the Excel Date Converter
- Choose the date system: "1900 (Excel / Google Sheets)" for modern workbooks, or "1904 (Legacy Mac)" for older Mac-originated files.
- Select the conversion direction: "Serial Number → Date" to decode a raw number, or "Date → Serial Number" to find the serial for a known date.
- Enter a serial number (e.g., 46201) or pick a date from the date picker.
- The result appears immediately, including the day of the week for date outputs.
- Click "Copy Result" to copy the converted value to the clipboard.
Why Use ToolForge’s Excel Date Converter
- Both date systems supported: the 1900 system (used by all modern Excel and Google Sheets workbooks) and the 1904 system (used in legacy Mac Excel files) are both available, so you can match whichever system your workbook actually uses.
- 1900 leap-year bug is handled: Excel incorrectly counts February 29, 1900 as day 60, which shifts every date on or after March 1, 1900 by one. The converter accounts for this discrepancy so your results match what Excel actually shows, not what a naive date calculation would produce.
- Bidirectional: convert from serial number to a readable date or from a date back to its serial number, useful both for debugging raw data and for constructing serial values to enter into formulas.
- Day-of-week display: date results include the day of the week (Monday, Tuesday, etc.), giving you an immediate sanity check that the conversion is correct.
Frequently Asked Questions
Why does Excel's date system have a leap-year bug?
The original Lotus 1-2-3 spreadsheet incorrectly treated 1900 as a leap year, and when Microsoft built Excel, they preserved this bug deliberately for compatibility. This means Excel counts February 29, 1900 as day 60, even though it never existed. Every date from March 1, 1900 onward is therefore one day higher in Excel's serial system than a strictly correct Julian Day calculation would give.
How do I find the serial number of a date in Excel?
Format any date cell as "Number" (Home → Number Format → Number) and the serial value is revealed. Alternatively, =DATEVALUE("2026-06-29") returns the serial number for a text-formatted date, and simply entering =TODAY() in a Number-formatted cell shows today's serial.
When would I need to convert a date serial number?
The most common scenarios are: (1) receiving CSV or API data where dates came through as integers rather than formatted strings; (2) writing VBA or Apps Script that passes date integers between systems; (3) debugging a formula that returns an unexpected number instead of a date because the cell is not formatted as a date type.
