Enter an Excel serial number to see the equivalent calendar date, or pick a calendar date to get its serial number back. Choose your conversion direction, select the Excel date system (1900 for Windows, 1904 for Mac), and the tool returns the converted date, day of week, time fraction, and a ready-to-use Excel formula.
Converted Result
--
Day of Week
--
Formatted Date
--
1900-System Serial
--
1904-System Serial
--
Excel Formula
--
Excel stores dates as sequential integers called serial numbers. In the default 1900 date system, January 1, 1900 is serial number 1, and each subsequent day adds 1. So January 1, 2024 is serial number 45292. This lets Excel perform arithmetic on dates (e.g. subtracting two dates to find the number of days between them).
The 1900 date system (default on Windows) counts January 1, 1900 as day 1. The 1904 date system (used in older Mac versions of Excel) starts from January 2, 1904, making it 1462 days behind the 1900 system. If you share workbooks between Windows and Mac Excel without adjusting the date system, dates can appear off by exactly 4 years and 1 day.
This is a deliberate legacy bug carried over from Lotus 1-2-3 for compatibility. Excel treats February 29, 1900 as a valid date (serial 60) even though 1900 was not actually a leap year. This means serial numbers 1–59 map correctly, serial 60 is a phantom date, and all serials from 61 onward are correctly aligned.
You can use =TEXT(serial_number, "mm/dd/yyyy") to display the date as formatted text, or simply format the cell containing the serial number as a Date in Excel's Format Cells dialog. For example, =TEXT(45292,"mm/dd/yyyy") returns "01/01/2024".
Yes. Excel represents time as a decimal fraction of a day. For example, 0.5 represents noon (12:00 PM). A serial number like 45292.75 means January 1, 2024 at 6:00 PM. You can use =TEXT(serial,"mm/dd/yyyy hh:mm:ss") to display both date and time together.
In the 1900 date system, Excel supports dates up to December 31, 9999, which corresponds to serial number 2,958,465. Dates before January 1, 1900 cannot be represented as serial numbers in the standard date systems and must be stored as text.
In Excel, go to File → Options → Advanced, then scroll down to the 'When calculating this workbook' section. If 'Use 1904 date system' is checked, your workbook uses the 1904 system; otherwise it uses 1900. You can also check this in Excel for Mac under Preferences → Calculation.
If two workbooks use different date systems (one uses 1900 and the other uses 1904), dates pasted between them will be off by 1,462 days (4 years and 1 day). Always ensure both workbooks use the same date system before sharing data, or manually add or subtract 1462 from the serial numbers to compensate.