Excel serial date converter: Excel date to number and back
Excel stores a date as the number of days since its epoch: 1 January 1900 is 1 and 1 January 2025 is 45658, and the decimal part is the time of day. Enter a serial number to get the date and time, or a date to get its serial in both the 1900 and the 1904 system.
How Excel stores dates
A date in Excel is an ordinary number formatted to look like a date. In the default 1900 date system, serial 1 is 1 January 1900 and each day adds 1, so 1 January 2025 is 45658 and 23 October 2026 is 46318. Because the date is a number, subtracting two dates gives the days between them.
The time of day is the fraction after the decimal point. Noon is 0.5, 6 a.m. is 0.25 and one hour is 1/24, about 0.041667. So 46318.5 is 23 October 2026 at 12:00. Excel serials carry no time zone and no daylight saving time; they are whatever the clock said when the value was typed or imported.
| Serial | Date and time (1900 system) |
|---|---|
| 46318 | 23 October 2026, 00:00 |
| 46318.25 | 23 October 2026, 06:00 |
| 46318.5 | 23 October 2026, 12:00 |
| 46318.75 | 23 October 2026, 18:00 |
| 46388 | 1 January 2027, 00:00 |
The 1900 system runs to serial 2958465, which is 31 December 9999. Serial 0 is shown as “1900-01-00”, and Excel does not display negative serials as dates.
The 29 February 1900 that never existed
1900 was not a leap year: it is divisible by 100 but not by 400. Excel’s 1900 system still counts a 29 February 1900 as serial 60. Microsoft explains that Lotus 1-2-3 had this error and Excel kept it so that files and formulas would work the same in both programs.
The effect is limited to the first two months of 1900. Serials 1 to 59 are 1 January to 28 February 1900, 60 is the fake leap day and 61 is 1 March 1900. From there on every date is right, and later century years such as 2100 are correctly treated as common years. Microsoft notes that WEEKDAY returns wrong values for dates before 1 March 1900. The converter marks serial 60 as a date that does not exist.
The 1900 and 1904 date systems
Early versions of Excel for Mac used the 1904 date system, which starts at 1 January 1904 as serial 0. Excel for Windows and current Excel for Mac default to the 1900 system, but any workbook can switch: in Windows, File > Options > Advanced > “Use 1904 date system”.
The two systems are 1,462 days apart. Microsoft’s own example is 5 July 2011, which is 40729 in the 1900 system and 39267 in the 1904 system. If dates copied from an old Mac workbook show up four years and one day early or late, the two workbooks use different systems. Add or subtract 1462 to fix them.
Google Sheets and LibreOffice
Google Sheets and LibreOffice Calc count from 30 December 1899 as day 0 and treat 1900 as a common year. For every date from 1 March 1900 on, their serial numbers are the same as Excel’s, which is why files move between the programs without shifting dates.
Before March 1900 they differ by one day. In Google Sheets serial 1 is 31 December 1899, while in Excel it is 1 January 1900. This only matters for historical data from the first two months of 1900 or earlier.
Excel date formulas
These work the same in Excel, Google Sheets and LibreOffice:
=DATE(2026,10,23)returns the serial 46318 for a year, month and day.=DATEVALUE("2026-10-23")turns a date written as text into its serial. The text must be in a format your locale recognizes.=TEXT(A1,"yyyy-mm-dd hh:mm")writes the serial in A1 as text, for example2026-10-23 18:00for 46318.75.=A1*1or=VALUE(A1)shows the serial behind a date; so does changing the cell format to General.=INT(A1)keeps the date and=MOD(A1,1)keeps the time fraction.
For a Unix timestamp in seconds, =A1/86400+DATE(1970,1,1) gives the serial, since 1 January 1970 is 25569. The Unix timestamp converter has the reverse formula. For day-of-year codes such as 26296, the Julian date converter has formulas that build on DATE.
Common mistakes with Excel serial dates
- Treating the serial as a day count from 1900. Because of the fake leap day, 46318 minus 1 is not the number of days since 1 January 1900. The actual count is 46316.
- Mixing date systems. A workbook set to 1904 reads every serial 1,462 days earlier. Check the setting before comparing numbers between files.
- Reading CSV exports as serials. A column of five-digit numbers in an exported file is often Excel dates that lost their format. Numbers around 46000 are dates in 2025 and 2026.
- Expecting a time zone. A serial with a fraction is a local clock reading. Convert to UTC yourself before comparing it with a timestamp.
More on the method behind the converter is on how we calculate.
Questions
How do I convert an Excel number to a date?
Format the cell as a date (Ctrl+1, then Date). The number does not change, only how it is shown. In the converter, enter the number to see the date, for example 46318 is 23 October 2026.
Why does Excel think 1900 was a leap year?
For compatibility with Lotus 1-2-3, Excel's 1900 system includes 29 February 1900 as serial 60, a day that never existed. Every serial from 61 (1 March 1900) on is one higher than a plain day count.
What is the difference between the 1900 and 1904 date systems?
The 1904 system starts at 1 January 1904 = 0 and was the default in early Excel for Mac. The same date is 1,462 days lower than in the 1900 system: 5 July 2011 is 40729 in one and 39267 in the other.
Do Google Sheets and Excel give the same serial numbers?
Yes for dates from 1 March 1900 on. Google Sheets and LibreOffice count from 30 December 1899 and treat 1900 as a common year, so before March 1900 their numbers are one day off Excel's.
What does the decimal part of an Excel date mean?
It is the time as a fraction of a 24-hour day: 0.5 is 12:00 and 0.75 is 18:00. 46318.75 is 23 October 2026 at 6 p.m. There is no time zone.