XL: The 1900 Date System vs. the 1904 Date System (180162)

MORE INFORMATION

The 1900 Date System

In the 1900 date system, the first day that is supported is January 1, 1900. When you enter a date, the date is converted into a serial number that represents the number of elapsed days since January 1, 1900. For example, if you enter July 5, 1998, Microsoft Excel converts the date to the serial number 35981.

By default, Microsoft Excel for Windows and Microsoft Excel for Windows NT use the 1900 date system. The 1900 date system allows greater compatibility between Microsoft Excel and other spreadsheet programs, such as Lotus 1-2-3, that are designed to run under MS-DOS or Microsoft Windows.

The 1904 Date System

In the 1904 date system, the first day that is supported is January 1, 1904. When you enter a date, the date is converted into a serial number that represents the number of elapsed days since January 1, 1904. For example, if you enter July 5, 1998, Microsoft Excel converts the date to the serial number 34519.

By default, Microsoft Excel for the Macintosh uses the 1904 date system. Because of the design of early Macintosh computers, dates before January 1, 1904 were not supported; this design was intended to prevent problems related to the fact that 1900 was not a leap year. Note that if you switch to the 1900 date system, Microsoft Excel for the Macintosh does support dates as early as January 1, 1900.

The Difference Between the Date Systems

Because the two Date Systems use different starting days, the same date is represented by different serial numbers in each date system. For example, July 5, 1998 can have two different serial numbers.

                      Serial number
   Date system        of July 5, 1998
   ----------------------------------

   1900 date system   35981
   1904 date system   34519
				

The difference between the two date systems is 1,462 days; that is, the serial number of a date in the 1900 Date System is always 1,462 days greater than the serial number of the same date in the 1904 date system. 1,462 days is equal to four years and one day (including one leap day).

Setting the Date System for a Workbook

In Microsoft Excel, each workbook can have its own date system setting, even if multiple workbooks are open. You can set the date system for a workbook by following these steps:

1. Open or switch to the workbook.
2. On the Tools menu (or Edit menu in Excel 2001 for Mac), click Options or Preferences. Then, click the Calculation tab.
3. To use the 1900 date system in the workbook, click to clear the 1904 Date System check box. To use the 1904 date system in the workbook, click to select the check box.
4. Click OK.

Note that if you change the date system for a workbook that already contains dates, the dates shift by four years and one day. For information about correcting shifted dates, see the "Correcting Shifted Dates" section in this article.

Problems Linking and Copying Dates Between Workbooks

If two workbooks use different date systems, you may encounter problems when you link or copy dates between workbooks. Specifically, the dates may be shifted by four years and one day.

To see an example of this behavior, follow these steps:

1. In Microsoft Excel, create two new workbooks (Book1 and Book2).
2. Use the steps in the "Setting the Date System for a Workbook" section to use the 1900 date system in Book 1. Use the 1904 date system in Book2.
3. In Book1, enter the date July 5, 1998.
4. Select the cell that contains the date, and click Copy on the Edit menu.
5. Switch to Book2, select a cell, and click Paste on the Edit menu.
   
   The date is pasted as July 6, 2002. Note that the date is four years and one day later than the date in step 3 because Book2 uses the 1904 date system.
6. In Book2, enter the date July 5, 1998. Select the cell that contains the date and click Copy on the Edit menu.
7. Switch to Book1, select a cell, and click Paste on the Edit menu.

The date is pasted as July 4, 1994. It has been shifted down by four years and one day because Book1 uses the 1900 date system.

Correcting Shifted Dates

If you link from or copy dates between workbooks, or if you change the date system for a workbook that already contains dates, the dates may be shifted by four years and one day. You can correct shifted dates by following these steps:

1. In an empty cell, enter the value 1462.
2. Select the cell. On the Edit menu, click Copy.
3. Select the cells that contain the shifted dates. On the Edit menu, click Paste Special.
4. In the Paste Special dialog box, click Values. Then, select either of the following option buttons.

      Select this     If
      --------------------------------------------------------------------
   
      Add             The dates must be shifted up by four years and one
                      day.
   
      Subtract        The dates must be shifted down by four years and one
                      day.
   					

5. Click OK.

Repeat these steps until all of the shifted dates have been corrected.

If you are using a formula to link to a date in another workbook, and if the date returned by the formula is incorrect because the workbooks use different date systems, modify the formula to return the correct date, for example:

   =[Book2]Sheet1!$A$1+1462
				

   =[Book1]Sheet1!$A$1-1462
				

In the formulas, 1,462 is added or deleted from the date value.

More Information in the Microsoft Knowledge Base

The Microsoft Knowledge Base contains several other articles that have information about using the 1900 date system and the 1904 date system in Microsoft Excel. These articles are listed as follows: