Excel and Julian date converter
Turn Excel serials, astronomical Julian Days, and ordinal YYDDD dates into calendar dates, and back again. Everything runs in your browser in UTC. Nothing is uploaded.
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How to convert a date
Use any box, then read the results below. Excel serial 45000 in the 1900 system is 15 March 2023. A fraction such as .5 is noon. Julian Day 2451545.0 is noon UTC on 1 January 2000. Ordinals 2023074 and 23074 are both the 74th day of 2023.
For a 5-digit YYDDD value, 00 through 49 mean 2000 through 2049, and 50 through 99 mean 1950 through 1999. If you enter only a day of year, fill in the year as well.
Frequently asked questions
What is an Excel serial number?
An Excel serial is a count of days. In the 1900 system, 1 is 1 January 1900 and 45000 is 15 March 2023. A fraction is the time of day, so 45000.5 is noon.
Why is Excel serial 60 not a real day?
Excel copied a Lotus 1-2-3 bug and treats 1900 as a leap year. Serial 60 is 29 February 1900, a day that never happened. Serial 61 is 1 March 1900. Every later serial matches the real calendar. The 1904 system does not include that fake day.
What is the 1904 date system?
The 1904 system, used by older Mac Excel, starts at 0 on 1 January 1904. For dates after February 1900 it is 1462 days behind the 1900 serial.
What are the two meanings of Julian date?
Astronomers mean the Julian Day, a running count of days from noon UTC on 1 January 4713 BCE. Julian Day 2451545.0 is noon UTC on 1 January 2000. Manufacturing and military dates often mean the day of the year instead, written as YYDDD or YYYYDDD. 23074 and 2023074 are both 15 March 2023. In YYDDD, 00 to 49 mean 2000 to 2049, and 50 to 99 mean 1950 to 1999.
Is the date sent anywhere?
No. The converter runs in your browser and uses UTC, so daylight saving time cannot move the day.