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Excel Date Converter

Convert Excel date serial numbers to readable dates and times, or any date and time to its Excel serial number. Supports the default 1900 system and the 1904 system, explains the 1900 leap-year bug, and converts whole lists at once.

Convert

Excel for Windows and current Mac versions use 1900 unless the workbook says otherwise.

Whole part = days, decimal part = time of day (0.5 = 12:00 PM).

Enter your values to see the result.
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How to use the Excel Date Converter

  1. Choose a direction: serial to date, date to serial, or many serials at once.
  2. Select the date system. Most workbooks use the 1900 system.
  3. Enter the serial number (decimals give the time), or pick a date and time.
  4. Press Convert; results also update as you type.
  5. Copy the result, or in batch mode download the converted list as CSV.

How Excel stores dates

Excel stores every date as a serial number: the count of days since the start of its date system, with the time of day as the decimal fraction. Formatting only changes how the number is displayed.

  • 1900 system: date = 1899-12-30 + serial days for serial ≥ 61; date = 1899-12-31 + serial days for serials 1–59; serial 60 is the fictitious February 29, 1900.
  • 1904 system: date = 1904-01-01 + serial days (serial 0 = January 1, 1904).
  • Converting between them: 1900 serial = 1904 serial + 1,462.
  • Time: fraction = (hours × 3,600 + minutes × 60 + seconds) ÷ 86,400.
  • Unix time: serial = unix seconds ÷ 86,400 + 25,569 (UTC).

Common Excel serial numbers

Date1900 system1904 system
January 1, 19001—
February 28, 190059—
March 1, 190061—
January 1, 19041,4620
January 1, 1970 (Unix epoch)25,56924,107
January 1, 200036,52635,064
January 1, 202545,65844,196
January 1, 202646,02344,561
December 31, 99992,958,4652,957,003

Tip: if dates imported from another workbook are exactly 4 years and 1 day off, one file uses the 1904 system and the other the 1900 system.

Frequently asked questions

How do I convert an Excel serial number to a date?

In the 1900 system, serial 1 is January 1, 1900 and each whole number adds one day. For serials 61 and above, the date is December 30, 1899 plus the serial in days; for example 45000 is March 15, 2023. In Excel itself, just format the cell as a Date.

Why does Excel think 1900 was a leap year?

Early Lotus 1-2-3 wrongly treated 1900 as a leap year, and Excel kept the same numbering for compatibility. Serial 60 is the non-existent February 29, 1900, so dates before March 1, 1900 are off by one day compared with other software.

What is the difference between the 1900 and 1904 date systems?

The 1904 system counts days from January 1, 1904 (serial 0) and was the default in old Mac versions of Excel. The same date has a serial 1,462 lower in the 1904 system than in the 1900 system. You can see which one a workbook uses under Excel Options › Advanced › 'Use 1904 date system'.

How are times stored in Excel?

Time is the decimal part of the serial, as a fraction of a 24-hour day. 0.5 is 12:00 PM, 0.25 is 6:00 AM and 0.75 is 6:00 PM, so 45000.75 is March 15, 2023 at 6:00 PM.

How do I convert a Unix timestamp to an Excel date?

Divide the Unix timestamp (seconds) by 86,400 and add 25,569, the 1900-system serial of January 1, 1970. The result is in UTC; add or subtract hours for your time zone. In Excel: =A1/86400+25569.

What is the largest date Excel supports?

December 31, 9999, which is serial 2,958,465 in the 1900 system. Excel cannot display negative serials, so dates before 1900 (or 1904) are stored as text.

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