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Open toolExcel Date Serial Converter
Convert raw Excel serial numbers (such as `46318.625`) into ISO-8601 dates, `HH:MM:SS` clock times, and Unix timestamps—or convert calendar dates back into 1900 and 1904 Excel serials.
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How Excel Serial Date-Time Numbers Work
Excel stores every date-time as a floating-point number: the integer part counts days from the workbook epoch (`1900-01-00` in the 1900 system, adjusted for the Serial 60 leap-year slot), and the fractional part represents `Seconds / 86400`.
UnixEpochSeconds = round((Serial1900 - 25569) * 86400); Serial1904 = Serial1900 - 1462.
Valid from Serial 1 (`1900-01-01`) through Serial 2,958,465 (`9999-12-31`).
Excel Date Serial Number & Fractional Time Reference Table
Key milestone Excel serial numbers (1900 date system) and common decimal time-of-day fractions.
| Excel Serial (1900) | Calendar Date / Time (UTC) | Unix Timestamp (s) | Notes |
|---|---|---|---|
| `1.0` | `1900-01-01 00:00:00` | `-2208988800` | First valid day in the Excel 1900 date system. |
| `60.0` | `1900-02-29` (Lotus bug) | N/A (synthetic day) | Excel's intentional 1900 leap-year compatibility slot. |
| `25569.0` | `1970-01-01 00:00:00` | `0` | Unix Epoch anchor (`Serial - 25569 = Unix Days`). |
| `45658.0` | `2025-01-01 00:00:00` | `1735689600` | Start of calendar year 2025. |
| `46023.5` | `2026-01-01 12:00:00` | `1767268800` | `.5` fraction equals exact 12:00:00 PM noon. |
| `46318.625` | `2026-10-23 15:00:00` | `1792767600` | `.625` fraction equals 15/24 of a day (3:00:00 PM). |
How to Convert an Excel Date Serial Number
Decode numeric date columns from CSV/XLSX imports in three steps.
Pick Serial -> Date or Date -> Serial
Choose whether you are decoding a numeric Excel value like `46318.625` or computing the serial for a target date.
Enter the serial number or ISO date-time
Include any decimal fraction (such as `.25` for 06:00 AM or `.75` for 06:00 PM) to resolve exact hours, minutes, and seconds.
Select 1900 or 1904 workbook epoch
Click Convert Excel Serial Date to inspect both 1900 and 1904 equivalents, Unix epoch seconds/milliseconds, and SQL/Python/JS conversion snippets.
Worked examples for Excel Date Serial Converter
Compare baseline and alternative runs for Excel Date Serial Converter before exporting the result.
Baseline example
Convert Excel date serial numbers to calendar dates, HH:MM:SS times, and Unix timestamps (or vice versa) with Lotus 1-2-3 1900 leap-year bug handling.
Comparison scenario
UnixEpochSeconds = round((Serial1900 - 25569) * 86400); Serial1904 = Serial1900 - 1462.
Boundary check before exporting
Valid from Serial 1 (`1900-01-01`) through Serial 2,958,465 (`9999-12-31`).
How to interpret the Excel Date Serial Converter output
Review the calculated output alongside your entered parameters and unit conventions.
Valid from Serial 1 (`1900-01-01`) through Serial 2,958,465 (`9999-12-31`).
Input limits, assumptions, and related tools
Check the model scope and boundary conditions before applying the numbers to a real project.
UnixEpochSeconds = round((Serial1900 - 25569) * 86400); Serial1904 = Serial1900 - 1462. Valid from Serial 1 (`1900-01-01`) through Serial 2,958,465 (`9999-12-31`).
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Open toolFrequently Asked Questions
Answers about using Excel Date Serial Converter and understanding its results.
Why does Excel show a number like 45658 or 46318 instead of a date?
Excel stores dates internally as sequential serial numbers where the integer portion counts days since January 1, 1900 (Serial 1) and the fractional decimal portion represents the fraction of a 24-hour day. When a cell's format is reset to 'General' or exported to CSV/JSON, the raw serial number appears.
What is the Excel 1900 leap year bug (Serial 60)?
The year 1900 was not a leap year (century years are only leap years if divisible by 400). However, Lotus 1-2-3 mistakenly treated 1900 as a leap year, and Excel intentionally replicated that behavior for backward compatibility. As a result, Serial 59 is 1900-02-28, Serial 60 is the non-existent '1900-02-29', and Serial 61 is 1900-03-01.
How do I convert an Excel date serial to a Unix timestamp in SQL, Python, or JavaScript?
For any date on or after March 1, 1900 (Serial >= 61) in the 1900 date system, subtract 25569 (the Excel serial for 1970-01-01) and multiply by 86,400 seconds per day: UnixSeconds = (ExcelSerial - 25569) * 86400.
Why are dates shifted by 4 years and 1 day (1,462 days) between two workbooks?
One workbook is using the 1900 date system and the other has 'Use 1904 date system' enabled. The 1904 system starts Serial 0 at January 1, 1904, creating an exact 1,462-day difference for dates after March 1, 1900.
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