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Excel Date Serial Converter Online
Free online tool · No signup · Runs in your browser
Convert calendar dates and fractional Excel serial numbers using the 1900 or 1904 date system.
Your data stays in this browser tool. No account or upload to a processing service required.
Instructions
- Choose the workbook date system and direction.
- Enter a YYYY-MM-DD date with optional HH:mm:ss.sss time, or a decimal serial.
- Convert and download the result.
Understanding your result
In the 1900 date system, serial 1 is January 1, 1900. In the 1904 system, serial 0 is January 1, 1904. Choose the system used by your workbook before converting; a valid serial can represent different dates under the two systems.
What to do if you have a problem
If dates are several years apart from expected values, check the date-system setting. Serial 60 in the 1900 system is a historical fictitious date and is reported explicitly. Do not replace it with a real calendar date without checking what the source intended.
What to know before using the result
No timezone conversion; arithmetic uses UTC calendar fields. Supports real dates from 1900 to 9999 and nonnegative serials (1900 starts at serial 1; 1904 at 0). Serial 60 in the 1900 system is explicitly reported as fictitious February 29, 1900. Fractions are rounded to milliseconds. A fictitious date cannot be entered as a real date.
These tools work with pasted text or supported CSV files rather than Excel workbook files. CSV exports contain values and do not preserve workbook formatting, formulas or multiple worksheets. Formula builders produce formula text to use in Excel. Data processing runs in the browser tool.
Try an example
1900 system: 59 = 1900-02-28; 60 = fictitious 1900-02-29; 61 = 1900-03-01. Add 0.5 for noon.
Summary
Use the converted date or serial with the date system selected for your workbook.