Excel Date Converter
Convert an Excel serial date (OADate) — days since 1899-12-30 — to a calendar date and Unix time.
Reviewed by the CalcCafe editorial team · Last updated 1 July 2026 · How we test our tools
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Your local time
ISO 8601
Relative
Unix seconds
Unix milliseconds
Current time updating:
How it works
Conversion: unixDays = serial − 25569, where 25569 is the days between 1899-12-30 and 1970-01-01.
Enter a value to convert it to a human-readable date, or click Use current time. Conversion is two-way and runs entirely in your browser.
Frequently asked questions
Why 1899-12-30, not 1900-01-01?
Excel intentionally treats 1900 as a leap year (it was not) for Lotus 1-2-3 compatibility, so its serial dates effectively count from 1899-12-30.
What is an OADate?
The OLE Automation date — used by Excel and COM — is a floating-point day count where the integer part is the day and the fraction is the time of day.
People also ask
How to do date conversion in Excel?
Excel stores every date as a serial number of days since 1899-12-30, so converting is mostly a matter of changing how that number is displayed or turning text into a real serial. To change the display, select the cells, press Ctrl+1, and pick a Date format or a custom code such as yyyy-mm-dd. To turn text into a date, use DATEVALUE(A1) or DATE(year, month, day), and to go the other way use TEXT(A1, "dd/mm/yyyy"). To get a Unix timestamp from a serial, use (A1 - 25569) * 86400, which is the same formula this converter applies.
How do I convert a DD.MM.YYYY date to YYYY/MM/DD in Excel?
If the cell already holds a real date, just change the number format: press Ctrl+1, choose Custom, and enter yyyy/mm/dd. If the cell holds text like 02.09.2026, rebuild it as a date with =DATE(RIGHT(A1,4), MID(A1,4,2), LEFT(A1,2)) and then apply the yyyy/mm/dd format to the result. You can also use Data, then Text to Columns, and choose the DMY date option to convert a whole column of text at once.
How to use DATEVALUE()?
DATEVALUE converts a date written as text into Excel's serial number, for example =DATEVALUE("2026-09-02") returns 46267, the number of days since 1899-12-30. The result looks like a plain number until you apply a date format to the cell. It interprets ambiguous strings like 02/09/2026 according to your Windows or macOS regional settings, so use an unambiguous yyyy-mm-dd string or the DATE(year, month, day) function when the day and month order matters.
How to format Excel cells to mm, dd, yyyy?
Select the cells, press Ctrl+1 (Cmd+1 on a Mac), choose Custom, and type mm/dd/yyyy or mm-dd-yyyy in the Type box, depending on the separator you want. This changes only how the underlying serial number is shown, so the cell still works in date arithmetic. If you need the text itself in that pattern, for example to concatenate it, use =TEXT(A1, "mm/dd/yyyy") instead.
How to convert string to date in mm dd yyyy format in Excel?
First turn the string into a real date serial, then apply the mm/dd/yyyy display format. For a string like 09/02/2026 that matches your regional settings, =DATEVALUE(A1) is enough; for other orders, parse the pieces with =DATE(RIGHT(A1,4), LEFT(A1,2), MID(A1,4,2)) or similar. Then select the result, press Ctrl+1, and set a custom format of mm/dd/yyyy so the serial number shows as a date.
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