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.