Excel Date Serial Number Converter
Paste an Excel (or Google Sheets) date serial number and instantly see the calendar date, UTC time, and Unix timestamp. Decimals are accepted for datetime values (e.g. 45292.5 = noon on 2024-01-01).
How Excel stores dates
Spreadsheet applications store every date as a plain number. The integer part is the number of days since a reference point; the fractional part encodes the time of day. Internally, the formula =A1 - A2 gives you the number of days between two dates because the subtraction is just ordinary arithmetic on these numbers.
The reference point for Excel (and Google Sheets, and LibreOffice) is effectively December 30, 1899 — a quirk introduced to maintain compatibility with Lotus 1-2-3, which incorrectly counted 1900 as a leap year. Every date from March 1, 1900 onward is therefore shifted by one day compared to a system that counts from January 1, 1900 correctly.
Useful reference serials
| Serial | Date |
|---|---|
| 1 | 1900-01-01 |
| 25569 | 1970-01-01 (Unix epoch) |
| 44927 | 2023-01-01 |
| 45292 | 2024-01-01 |
| 45658 | 2025-01-01 |
| 46023 | 2026-01-01 |
Converting serials in Excel, Sheets, and Python
Frequently asked questions
What is an Excel date serial number?
Excel stores dates as plain numbers called serial numbers. Serial 1 represents January 1, 1900 and each subsequent day adds 1. Serial 44927 is January 1, 2023. Times are stored as the fractional part: 0.5 = noon, 0.25 = 6 AM, etc. This makes date arithmetic trivial — subtracting two serial numbers gives the number of days between them.
What is the 1900 leap year bug?
Excel (and Lotus 1-2-3, which Excel mimicked for compatibility) incorrectly treats 1900 as a leap year. As a result, serial 60 is assigned to 'February 29, 1900' — a date that never existed. Every date from March 1, 1900 onward is therefore off by one from what you would expect. This tool accounts for the bug automatically: serial 25569 correctly maps to January 1, 1970 (the Unix epoch).
Does this work with Google Sheets?
Yes. Google Sheets uses the same date serial system as Excel (with the 1900 compatibility mode on by default). LibreOffice Calc also uses the same convention. All three tools show the same serial numbers for the same dates.
How do I get the serial number for a date in Excel?
Select a date cell and format it as 'Number' (Ctrl+1 → Number category). The value in the cell is the serial number. Alternatively, use =DATEVALUE("2024-01-01") to convert a date string to its serial number, or wrap any date formula in =INT() to strip the time portion.
What serial number is today?
Click the 'Now' button in the converter above to see today's serial number. As a rough guide: 44927 = 2023-01-01, 45292 = 2024-01-01, 45658 = 2025-01-01, 46023 = 2026-01-01.
Can I use decimal serial numbers to represent a specific time?
Yes. The integer part is the date; the decimal is the fraction of the day. For example, 45292.5 = noon on January 1, 2024. This converter accepts fractional serials and shows the exact time in the output.