What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Excel’s 1900 and 1904 date systems assign different serial numbers to the same calendar date. Their values differ by exactly 1,462 days: a 1900-system serial is 1,462 higher than its 1904-system equivalent. If dates shift when copied between workbooks, check each workbook’s date-system setting before changing values.
What the 1900 and 1904 date systems mean
Excel stores dates as serial numbers and represents times as fractions of a day. A cell’s number format controls how that value appears; it does not change the underlying serial. The date system is a workbook-level setting that determines how Excel interprets those serials. The workbook file format also records whether the 1904 system is in use.
As an Amazon Associate I earn from qualifying purchases.
The systems use different date origins, but they do not represent different calendars. For the same date, the serial in the 1900 system is 1,462 greater than the serial in the 1904 system. Microsoft’s example is July 5, 2011: serial 40729 in the 1900 system and 39267 in the 1904 system. Microsoft describes the difference as four years and one day, including a leap day. Microsoft’s overview of Excel date systems explains the relationship.
Outdated Drivers Are Slowing You Down
One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchWindows Errors? Fix Them Before They Spread
Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallCompare the systems
| What to compare | 1900 system | 1904 system |
|---|---|---|
| Date origin | Uses the 1900 date system. | Uses a date origin four years and one day later than the 1900 system. |
| Serial for July 5, 2011 | 40729 (Microsoft example). | 39267 (Microsoft example). |
| Workbook setting | The workbook interprets serials using the 1900 system. | The workbook interprets serials using the 1904 system. |
The serial examples and the 1,462-day difference are from Microsoft Support.
Why dates can change when you copy between workbooks
When copying dates from one workbook to another, Excel may convert them between date systems. Depending on its conversion settings, it may instead prompt you. If serial values are retained but interpreted using the other system, the displayed dates can be 1,462 days apart. This is why a date can appear roughly four years and a day off—or change in the opposite direction—after a copy.
Chart dates need separate attention: Microsoft cautions that dates in charts copied from a 1904-system workbook do not convert automatically in the same way as ordinary copied dates. Microsoft’s copy-and-paste guidance describes this caveat.
Rank #2
- Used Book in Good Condition
How to check and correct a date-system mismatch
- Check both workbooks. Compare the source and destination date-system settings before editing the affected values.
- Find the setting in Windows Excel. In newer versions, go to File > Options > Advanced > When calculating this workbook, then check whether Use 1904 date system is selected. Menu labels can vary by version.
- Find the setting on Mac. Microsoft’s cited instructions place the checkbox in Excel preferences under calculation settings; the exact labels can vary by version. See Microsoft’s date-system and formatting instructions.
- Choose the destination system deliberately. Consider the workbook’s other dates and formulas before changing its setting. For the copy-and-paste scenario Microsoft describes, it recommends converting pasted data to the 1900 system.
- Correct already-misinterpreted serials once, in the right direction. To convert a 1904-system serial to 1900, add 1,462. To convert from 1900 to 1904, subtract 1,462. Do not both switch the workbook’s date system and apply the offset to the same values; that can adjust them twice.
- Inspect charts separately. Check chart dates after moving data from a 1904-system workbook because they may need a separate correction.
Which system does Excel use by default?
Microsoft says newer Excel versions use the 1900 system. Its support documentation also describes 1900 as the Windows default and 1904 as the historical Mac default. That history does not mean that every current Mac installation uses 1904; check the setting in the specific workbook. The underlying file format’s Date1904 flag documents whether a workbook uses the 1904 system: Microsoft’s workbook-format specification.
Excel’s 1900 leap-year compatibility quirk
Excel preserves the assumption that 1900 was a leap year to match the date-serial system used by Lotus 1-2-3. The narrow consequence Microsoft identifies is that WEEKDAY can return incorrect values for dates before March 1, 1900. Microsoft says other leap years, including 2100, are handled correctly. This historical compatibility choice does not mean ordinary modern dates are generally wrong. See Microsoft’s explanation of the 1900 leap-year behavior.
Quick Recap
Best Value
- The Microsoft Office 365 Bible: The Most Updated and Complete Guide to Excel, Word, PowerPoint, Outlook, OneNote, OneDrive, Teams, Access, and Publisher from Beginners to Advanced
- ABIS BOOK
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
