Excel Serial Date Converter
Convert Excel serial date numbers to real dates and back, for the 1900 and 1904 systems, with the serial 60 leap-year bug handled. Free and in-browser.
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What is Excel Serial Date Converter?
The Excel Serial Date Converter turns Excel date serial numbers into real calendar dates and back, supporting both the 1900 (Windows) and 1904 (legacy Mac) systems and faithfully reproducing the famous serial-60 leap-year bug.
Key Benefits
- Decode raw serial numbers from CSV, database, and API exports.
- Correct 1900-system math, including the missing 1900-02-29.
- Decimal serials reveal the time of day, not just the date.
- Avoid the four-year shift when mixing Windows and old Mac files.
- Instant offline conversion - no spreadsheet required.
Common Use Cases
- •Cleaning dates out of raw CSV and database dumps.
- •Debugging one-day date offsets in legacy exports.
- •Understanding data migrated from old Mac spreadsheets.
- •Building import scripts that must output real Excel serials.
How to Use the Excel Serial Date Converter
- Pick the date system: Keep 1900 for normal Windows-created files; use 1904 only for legacy Mac spreadsheets.
- Serial to date: Type the serial number, such as 43831, to see the matching calendar date and weekday.
- Date to serial: Pick a date to see the serial number Excel would store for it.
- Watch for serial 60: In the 1900 system, serial 60 is the fake 1900-02-29 - the tool explains it instead of guessing.
Key Features
- Converts serial numbers to dates and dates to serial numbers.
- Supports both the 1900 (Windows) and 1904 (legacy Mac) systems.
- Reproduces the serial 60 fake 1900-02-29 leap-year bug faithfully.
- Decimal serials decode into time of day.
- Shows the weekday for every converted date.
- Instant, offline conversion with no spreadsheet required.