Excel serial numbers such as 45292 to dates and back, 1900 or 1904 system, with times
Runs in your browser. Nothing you type is sent anywhere. Updated on 24 Oct 2026.Excel stores a date as the number of days since the start of 1900, with the time as a fraction of a day. Serial 45292 is 1 January 2024 and 45292.75 is 18:00 that day. The 1904 system used by older Mac workbooks gives the same date a serial 1,462 lower.
Choose the Date system: 1900 (Windows) or 1904 (Mac).
On the Convert tab, type a serial number such as 45292.75, or a date such as 2024-01-01 18:00.
Read the result, with the weekday and time of day for a serial.
Use the List tab for a column of values, or Time fraction to turn 18:30 into a fraction of a day.
This converter reads an Excel date serial number and shows the calendar date, the weekday and the time, or takes a date and gives the serial Excel would store. Type 45292 to get 1 January 2024; type 2024-01-01 18:00 to get 45292.75. A number is read as a serial and anything else as a date, so there is no mode to set. Times can also be converted on their own: 18:30 is the fraction 0.7708333333.
Both of Excel's date systems are supported. The 1900 system, the default on Windows, counts 1 January 1900 as day 1. The 1904 system, used by older Mac workbooks and still selectable in Excel's options, counts 1 January 1904 as day 0. Microsoft documents the gap between them as 1,462 days, and the page shows the other system's serial for every result, which explains dates that are four years and one day out after copying between workbooks.
The 1900 system keeps a known mistake. Lotus 1-2-3 treated 1900 as a leap year, and Excel copied it for compatibility, so serial 60 is 29 February 1900, a day that never existed. The converter shows that date as Excel does and flags it. Serials 1 to 59 are one day earlier than a naive count from 30 December 1899 gives, and the weekday shown is the real one, not the one Excel's WEEKDAY function reports.
The batch box converts a pasted column in one go and copies back as tab-separated text. What it does not do: apply time zones, since a serial has no zone, read a workbook, or handle dates before 1900. Everything runs in your browser.
In the default 1900 date system, 45292 is Monday 1 January 2024. The number counts days, so 45293 is 2 January. In the 1904 date system the same number would be 1,462 days later, 2 January 2028, which is why knowing the workbook's date system matters.
Excel stores every date as a serial number and only shows it as a date when the cell has a date format. When the format is lost, for example in a CSV export or after pasting values, the bare number appears. Converting the number here, or setting the cell format back to Date, recovers it.
Lotus 1-2-3 wrongly treated 1900 as a leap year, and Excel kept the same serial numbers so worksheets could move between the two programs. Serial 60 is therefore a date that never happened. Microsoft says fixing it would shift almost every stored date by one day, so it stays.
The 1900 system counts from 1 January 1900 and is the Windows default. The 1904 system counts from 1 January 1904 and came from early Mac Excel. Microsoft documents that the same date's serial is always 1,462 higher in the 1900 system than in the 1904 system.
The time is the fraction after the decimal point: the share of a 24-hour day that has passed. 0.5 is noon, 0.75 is 18:00 and 0.7708333333 is 18:30. The converter rounds to the nearest millisecond and shows milliseconds only when they are not zero.
Yes. Paste the column into the batch box, one value per line. Numbers become dates and dates become serial numbers, in the date system you have chosen. Copy the result as tab-separated text and paste it next to the original column in your spreadsheet.
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Also works as: Excel Serial Number to Date.