Excel Date Origin: 1900 vs. 1904 Systems

Excel’s default date origin on Windows is the 1900 date system: January 1, 1900 is serial number 1, and each later day increments the number by one. Excel also supports a 1904 date system, in which January 1, 1904 is serial 0; which origin applies depends on the workbook setting.

What Excel’s date origin means

Excel generally stores a date as a number rather than as a special text string. In the 1900 system, the whole-number part represents days counted from the system’s starting point. A cell may show a calendar date, but its underlying value is numeric. That is why dates can be added, subtracted, sorted, and used in calculations.

The date origin is the reference point for interpreting those numbers. It is not the date when you created the workbook, the date your computer was set up, or a setting that changes how every workbook on every computer works. The selected date system belongs to the workbook. Two workbooks can therefore interpret the same serial number as different calendar dates.

Formatting affects what you see, not the stored serial itself. A value such as 45292 can appear as a date, a plain number, or a date and time depending on the cell’s number format. Changing the format does not change the underlying number, just as changing a number format from currency to general does not alter the amount.

The 1900 date system and its leap-year quirk

The 1900 system is the default for Excel workbooks on Windows and the system most people encounter. Its ordinary early dates are straightforward: serial 1 is January 1, 1900; serial 31 is January 31, 1900; and serial 59 is February 28, 1900. Serial 61 is March 1, 1900.

Serial 60 is the exception. Excel treats it as February 29, 1900, even though that date never occurred. The Gregorian calendar does not make 1900 a leap year because century years are leap years only when divisible by 400. Excel retains this fictitious day for compatibility with Lotus 1-2-3, an earlier spreadsheet program whose date handling included the same error. Preserving it helped avoid changing date-related calculations and data when users moved spreadsheets between programs.

This quirk matters mainly when working with dates near the start of 1900 or when exchanging serial values with software that follows the calendar strictly. For modern dates, the extra serial does not make a normal calendar date wrong; it is part of how Excel keeps its numbering aligned with the historical compatibility choice.

The 1904 date system

In the 1904 system, serial 0 represents January 1, 1904. This system is associated with older Macintosh spreadsheet conventions and remains available in Excel for compatibility. It is not an alternative way of formatting a date: it changes the relationship between serial numbers and calendar dates throughout that workbook.

The two systems are separated by 1,462 days. As a result, the same serial number interpreted under each system represents dates 1,462 days apart. For example, a serial number that represents January 1, 2024 in the 1900 system represents January 2, 2028 in the 1904 system. Conversely, a calendar date transferred between systems can have serial values that differ by 1,462.

The 1904 system was historically useful for early Mac spreadsheets, including when negative date values were a concern. Today, most Windows workbooks use the 1900 system, and the 1904 system is usually relevant when maintaining older files or exchanging workbooks across platforms. A Mac version of Excel can work with either system; a Mac computer does not automatically mean every workbook uses 1904.

How date and time serials work

Excel stores times as fractions of a day. One half is noon, one quarter is 6:00 a.m., and one twenty-fourth is one hour. A date-and-time value combines the whole-day count with the time fraction. For instance, in a workbook using the 1900 system, January 1, 2024 at noon is represented by 45292.5: 45292 for the date and 0.5 for the time.

This numeric design makes common calculations possible. Subtracting one date serial from another gives the number of elapsed days, provided both values use the same date system and are valid date values. Adding 7 to a date serial moves it forward by seven days. Subtracting two date-and-time values gives an elapsed duration in days, so a result of 0.5 means twelve hours.

Because a date is a number, a cell can appear to contain a surprising value if it is formatted as General or Number rather than Date. The reverse can also happen: a number may display as a date if a date format is applied. If the displayed result looks wrong, check both the cell’s number format and the workbook’s date system before assuming the stored value has changed.

How to check or change a workbook’s date system

In Excel for Microsoft 365 on Windows, check the workbook setting at File > Options > Advanced. Under When calculating this workbook, look for Use 1904 date system. The box is generally clear for the standard 1900 system. This is a workbook-level option, so check it in the file whose dates you are investigating rather than relying on another workbook’s setting.

Changing the setting can shift how existing date serials display. Do not toggle it casually in a workbook with dates, formulas, or imported data: a date that was correct under the old system may appear 1,462 days away under the new one. Make a copy first, and verify representative dates and calculations after any change.

On Excel for Mac, the equivalent option is available in Excel’s preferences or settings under Calculation, although the menu wording can vary by release. Excel for the web may not offer the same control for changing the workbook’s date system, so use the desktop app when you need to inspect or change that setting. Opening a workbook on a Mac does not, by itself, convert its date system.

Why dates shift when workbooks are copied

A common source of confusion is copying dates between workbooks that use different systems. Excel may adjust dates when transferring cells between workbooks, but the result can depend on the operation and how the data is transferred. Copying and pasting cells, copying only displayed text, moving data through a CSV file, and passing raw serial numbers to another program are not necessarily equivalent.

CSV files do not preserve an Excel workbook’s date-system setting or cell formatting. A CSV generally contains text or numeric values, so the receiving program must interpret them. If a CSV contains a serial such as 45292, another application may treat it as an ordinary number, or it may apply a different date origin. If it contains a date written as 1/2/2024, regional settings can also affect whether that means January 2 or February 1.

When exchanging date data, reduce ambiguity by checking sample records at both ends. If possible, use an unambiguous date representation such as an ISO-style year-month-day value, and confirm how the receiving program parses it. For a spreadsheet-to-spreadsheet transfer, check the date-system setting in both workbooks and verify several known dates rather than relying on a single sample.

Common date-origin problems and limitations

The date system is only one reason a date may look wrong. Excel may interpret typed or imported text according to the computer’s regional date conventions. A value such as 03/04/2024 is ambiguous without knowing whether the order is month/day/year or day/month/year. A date stored as text may also fail to behave like a genuine numeric date when sorted or used in arithmetic.

Other useful checks include:

Inspect the cell value and format: Switch temporarily to General or Number to see whether the value is a serial number, while remembering that this does not identify the date system by itself.
Check for text: If changing the number format does not affect the display and arithmetic behaves unexpectedly, the entry may be text rather than a date serial.
Look for a workbook-system mismatch: If many dates are off by exactly 1,462 days, the 1900-versus-1904 setting is a strong possibility.
Review imported data: Confirm the source’s date order and whether it supplies calendar text, a serial number, or a timestamp.

Excel’s standard date systems do not provide ordinary calendar-date handling for dates before their respective starting ranges. In particular, the 1900 system has special behavior around its earliest dates, and dates before 1900 are not handled like modern dates by normal worksheet date calculations. If a project needs historical dates earlier than Excel can represent reliably, store and process them using a method designed for that range rather than assuming a displayed string will work as a genuine Excel date.

Excel date serials also do not include a time zone. A value representing 9:00 a.m. is simply a date plus a fraction of a day; Excel does not know whether it means local time, UTC, or another zone. For schedules or data spanning time zones, record the zone separately and define any conversion rules explicitly.

Frequently Asked Questions

What is Excel’s default date origin?
For Excel workbooks on Windows, the default is the 1900 date system. January 1, 1900 is serial 1, with Excel’s historical exception for the fictitious February 29, 1900 at serial 60.

Is Excel’s date origin January 1, 1900 or December 30, 1899?
For ordinary dates in the 1900 system, Excel describes serial 1 as January 1, 1900. Some technical explanations use December 30, 1899 as an effective base to account for numbering and the leap-year compatibility bug. For practical work, use the workbook’s date system and remember that serial 60 is the special case.

Why is my Excel date off by 1,462 days?
The workbook may be using the other date system. The 1900 and 1904 systems differ by 1,462 days, so compare the workbook settings and check known dates before changing anything.

Does Excel for Mac always use the 1904 date system?
No. Excel for Mac can open workbooks using either system. The date system is a workbook setting, not a rule determined solely by the computer’s operating system.

Can I change a workbook from 1904 to 1900?
Yes, the desktop version provides a workbook setting for this, but changing it can make existing dates display differently. Save a copy first and validate dates and calculations after the change.

Does Excel store a time zone with a date?
No. Excel stores a date-and-time serial without a time-zone designation. Keep the time zone in a separate field or document it another way when it matters.

Try it: the Date Difference Calculator: days, months, years and weekdays between two dates, with the DATEDIF formulas.

More in How-to basics

Sources: Function behaviour and menu paths: Microsoft Support documentation for Excel. Method & sources

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