Excel’s 1900 and 1904 date systems assign different serial numbers to the same calendar date. The 1900-system serial is exactly 1,462 higher than the 1904-system serial. If dates shift by about four years when moved between workbooks, the workbooks may use different systems—not different date formats.
What the 1900 and 1904 date systems mean
Excel stores dates as serial numbers and times as fractions of a day. A cell’s date format controls how its value appears; it does not change the underlying serial. The workbook’s date-system setting determines how Excel interprets that serial as a calendar date. Both systems represent calendar dates, but count from different origins.
For example, Microsoft gives July 5, 2011 as serial 40729 in the 1900 system and 39267 in the 1904 system. The 1900-system value is 1,462 greater. Microsoft describes that difference as four years and one day, including a leap day. Microsoft Support: Date systems in Excel
Compare the systems
| Detail | 1900 system | 1904 system |
|---|---|---|
| Serial relationship | For the same date, its serial is 1,462 greater than in the 1904 system. | For the same date, its serial is 1,462 less than in the 1900 system. |
| Example: July 5, 2011 | 40729 (Microsoft Support example) | 39267 (Microsoft Support example) |
| Default context | Used by newer Excel versions; Microsoft also identifies it as the Windows default. | Historical default on Mac Excel; do not assume current Mac installations use it. |
| Workbook setting | A workbook uses one date system, recorded in its file settings. Excel for Windows and Mac support both systems. | |
Sources: Microsoft Support and Microsoft’s Excel file-format specification.
Why dates can shift when copied between workbooks
If two workbooks use different date systems, the same serial number can be interpreted as a date 1,462 days apart. Excel may automatically convert copied dates between workbooks; depending on conversion settings, it may instead prompt. If the values remain in the other system without conversion, dates can appear about four years and one day off.
Microsoft cautions that chart dates copied from a 1904-system workbook do not convert automatically in the same way as ordinary copied dates. Check chart axes and plotted date values separately if a chart appears shifted. Microsoft Support: Date systems in Excel
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Check which date system a workbook uses
In newer Excel for Windows, open File > Options > Advanced, then look under When calculating this workbook for Use 1904 date system. On Mac, Microsoft’s cited instructions put the checkbox in Excel preferences under calculation settings. Labels and locations can vary by Excel version; consult Microsoft’s date-system and format instructions if your menus differ.
The setting belongs to the workbook, not merely to the cell’s display format. Changing a date format alone will not correct serial values interpreted under the wrong system.
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Safely correct dates that are already shifted
- Compare both workbooks’ settings. Check whether the source and destination use different date systems before changing values.
- Choose the destination system deliberately. Consider the workbook’s other dates and formulas before changing its setting. For the copy-and-paste scenario described in its guidance, Microsoft recommends converting pasted data to the 1900 system.
- Apply the offset only if the serials need conversion. To convert a 1904-based serial to the 1900 system, add 1,462. To convert a 1900-based serial to the 1904 system, subtract 1,462.
- Check the result and charts. Verify representative dates against the intended calendar values, and inspect chart dates separately.
Avoid changing the workbook’s date system and applying the offset to the same values: doing both can shift them twice. Microsoft’s offset relationship and copy/paste guidance are documented in Date systems in Excel.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.The 1900 leap-year compatibility quirk
Excel preserves a historical assumption that 1900 was a leap year to remain compatible with Lotus 1-2-3’s date serial system. In the narrow case of dates before March 1, 1900, Microsoft says the WEEKDAY function can return incorrect values. Microsoft says other leap years, including 2100, are handled correctly; this quirk does not mean ordinary modern dates are generally wrong. Microsoft Learn: Excel incorrectly assumes that the year 1900 is a leap year
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