# Difference between Excel date systems

Two different date systems used in Excel are 1900 date system and Excel 1904 date system. Click the following link to learn more about Excel 1900 date system and Excel 1904 date system and how to change Excel date systems.

Following table shows the difference between Excel 1900 date system and Excel 1904 date system.

Excel Date System Start Date Start Serial Number
1900 date system January 1, 1900 1
1904 date system January 1, 1904 0

Let us consider a sample date, December 5, 2021. Following two images show the serial number which represents the date December 5, 2021 in Excel 1900 date system and Excel 1904 date system respectively.  Sample date Excel date system Serial number
December 5, 2021 1900 date system 44535
December 5, 2021 1904 date system 43073

Let us find the difference between the date serial numbers when 1900 date system is used and 1904 date system is used. The difference between date serial numbers for the sample date December 5, 2021 when 1900 date system is used and when 1904 date system is used is 44535-43073 = 1462. Means that the difference in number of days between 1900 date system and 1904 date system is 1,462 days (four years and one day).