Excel Serial Date Converter

Q: What is an Excel serial date?

A number where **1 = 1900-01-01** (1900 system). The integer is days; the decimal is the time fraction (0.5 = noon). 45251.61 ≈ 2023-11-24 14:38.

Q: What is the Excel 1904 date system?

The **1904 system** used by legacy Mac Excel counts from **1904-01-01**. Serial 1 in 1904 ≈ serial 1462 in 1900 — the two systems differ by 1,462 days.

Excel stores dates as serial numbers: the integer part is days since the epoch and the fraction is the time of day. In the 1900 system, day 1 is January 1, 1900 (with a famous leap-year bug making 1900 a leap year). The 1904 system (Mac legacy) counts from January 1, 1904.

This converter returns the Excel serial (1900), the 1904 serial, and the fractional time-of-day component for any date, so you can debug CSVs, generate spreadsheet values, or decode a serial number you received from a colleague.

Timezone:

Enter a date-time above to see the conversion results.

Excel Serial Date Converter Quick Reference

Format	Pattern / Description	Example 1	Example 2
Excel 1900 System	Days since 1900 (Adjusted)	46247.6041666667	46023.0000000000
Excel 1904 System	Days since 1904 (Mac)	44785.6041666667	44561.0000000000

* Examples are rendered in UTC for the fixed sample instants above.

When to Use Excel Serial Date

CSV & spreadsheet import

When reading Excel exports, raw date columns arrive as serial numbers like `45251.61`. Convert them back to readable dates to verify your import.

Generating Excel values

APIs that write to Excel-compatible formats need serial dates. Compute the serial for a date before emitting cells.

Accounting & legacy systems

Many accounting and ERP systems store dates as Excel-style serials. Decode exported values without opening Excel.

Frequently Asked Questions

What is an Excel serial date?

A number where 1 = 1900-01-01 (1900 system). The integer is days; the decimal is the time fraction (0.5 = noon). 45251.61 ≈ 2023-11-24 14:38.

What is the Excel 1904 date system?

The 1904 system used by legacy Mac Excel counts from 1904-01-01. Serial 1 in 1904 ≈ serial 1462 in 1900 — the two systems differ by 1,462 days.

Why does Excel think 1900 was a leap year?

Lotus 1-2-3 (Excel's ancestor) had a bug treating 1900 as a leap year, and Excel preserved it for compatibility. Excel serials for dates after Feb 28, 1900 are correct; before that they are shifted.

How do I convert a serial number to a date?

Paste the raw number (e.g. `45251.61`) into the converter. The engine interprets it as a serial date and returns the full calendar date and time.

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