Excel Date Converter
Convert Excel serial numbers like 45000 into real dates - and dates back into serials. Handles times and both date systems.
Serial → Date
2023-03-15
Date → Serial
45000
How Excel Stores Dates
Excel represents every date as a serial number: the count of days since its epoch. January 1, 1900 is serial 1, and each later day adds one. Times live in the decimal part - 0.5 is noon, 0.75 is 6 PM. When a cell loses its date formatting you see the raw serial, which is why a date can suddenly look like 45000.
The 1900 Leap-Year Bug
Serial 60 maps to February 29, 1900 - a date that never existed. Lotus 1-2-3 treated 1900 as a leap year by mistake, and Excel intentionally kept the bug so old spreadsheets kept working. Every serial from 61 onward is offset by that ghost day.
Frequently Asked Questions
Excel stores dates as serial numbers - the count of days since the epoch (January 1900 by default). When a cell loses its date format, you see the raw serial. 45000 is March 15, 2023.
Windows Excel counts from January 1, 1900; classic Mac Excel counted from January 1, 1904. The same serial differs by 1,462 days between systems. Modern files almost always use 1900.
February 29, 1900 - a date that never existed. Lotus 1-2-3 wrongly treated 1900 as a leap year and Excel preserved the bug for compatibility. This tool flags it.
As the fractional part of the serial: .5 is noon, .75 is 6 PM. A value like 45000.25 means March 15, 2023 at 6:00 AM.