Excel Date (OADate) Converter
Convert Excel's serial date number (OADate) to a readable date and Unix timestamp, and back.
Excel Date ⇄ Timestamp
Runs entirely in your browserType in either field — the other updates live.
What is an Excel Serial Date?
Excel (and the underlying OLE Automation Date / OADate format) stores dates as a floating-point number of days since December 30, 1899. The integer part is the day; the fractional part is the time of day.
For example, 45839.55 is roughly 45,839 days after December 30, 1899 (a date in 2025), at about 13:12 into that day.
- Integer part = days since December 30, 1899
- Fractional part = time of day (0.5 = noon)
- Also called OADate (OLE Automation Date) outside of Excel
- Offset from Unix epoch: 25,569 days
Excel Date Format
Subtract 25,569 and multiply by 86,400,000 to get Unix milliseconds.
How do I convert an Excel date number to a real date?
Paste the serial number into the converter above. It subtracts 25,569 (the day offset between Excel's epoch and the Unix epoch) and converts the remaining days to a Unix timestamp.
Frequently Asked Questions
OADate format uses the exact same day-count system as Excel, so this converter works for both interchangeably.
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