Spreadsheet Formulas

Excel & Google Sheets ↔ Epoch Converter

Translate the serial numbers Excel and Google Sheets use internally into Unix timestamps and human-readable dates — or generate serial numbers from any date.

Serial Number → Date & Epoch

Days since Dec 30, 1899 (fraction represents time)

Enter Excel Serial Number

Example: 45000.5 represents noon on March 15, 2023

1904 Date System (Legacy macOS Excel)

Timezone Format

Date (Local):–

Unix Seconds:–

UTC ISO 8601:–

Relative Time:–

Date → Excel Serial Number

Pick any date and time to compute the Excel serial float

Date and Time

Excel Serial (1900 system):–

Unix Seconds:–

Spreadsheet Formulas:

Excel to Epoch: =(A1 - 25569) * 86400

Epoch to Excel: =(A1 / 86400) + 25569

How Excel Stores Dates

Excel stores dates as floating point serial numbers, representing the number of days elapsed since December 30, 1899. The fractional portion represents the fraction of a day (e.g., 0.5 = 12:00 noon, 0.25 = 6:00 AM).

The Famous 1900 Leap Year Bug

For backwards compatibility with Lotus 1-2-3, Microsoft Excel intentionally retained a bug where the year 1900 is treated as a leap year. Day 60 is recorded as February 29, 1900 — a date that never actually existed in the Gregorian calendar! The baseline constant 25569 accounts for this discrepancy when aligning with the 1970 Unix epoch.