Excel Serial Date & Unix Converter
Convert Excel serial dates using 1900 or 1904 systems and compare Unix timestamps.
Enter your values to see a result.
What is an Excel serial date?
Excel stores many dates as numbers of days from an epoch; fractions represent time of day. The common Windows 1900 system contains a historical fictitious leap day (serial 60). The 1904 system uses a different epoch, meaning the same calendar date has a different serial value.
Worked example
In the 1900 system, serial 1 is January 1, 1900; serial 60 is an imaginary February 29, 1900. Serial 45000 falls in March 2023. Switching to 1904 changes the interpretation.
Important assumptions and limitations
Unix timestamps are counted in seconds from 1970-01-01 00:00 UTC, unlike Excel serials. This calculator consistently treats conversion times as UTC.
How to use this tool
Enter valid input in the fields above and run the calculation or conversion. Review the displayed result, assumptions and any warnings before reusing the output. Where available, download or copy the result directly from your browser.
Frequently asked questions
Is this tool free?
Yes. It works without an account or registration.
Does the tool require a server?
The calculation runs in your browser with local JavaScript. A network connection is only needed to load the website.
Can I use the result professionally?
Check important results against a trusted source, especially for financial, legal and tax decisions. See the stated assumptions for this tool.