Entering Dates and Times into Your Worksheets

Excel treats dates and times as special types of numeric values. Typically, these values are formatted so that they appear as dates or times because we humans find it far easier to understand these values when they appear in the correct format. If you work with dates and times, you need to understand Excel’s date and time system.

Entering date values

Excel handles dates by using a serial number system. The earliest date that Excel understands is January 1, 1900. This date has a serial number of 1. January 2, 1900, has a serial number of 2, and so on. This system makes it easy to deal with dates in formulas. For example, you can enter a formula to calculate the number of days between two dates.

Most of the time, you don’t have to be concerned with Excel’s serial number date system. You can simply enter a date in a familiar date format and Excel takes care of the details behind the scene.

For example, if you need to enter June 1, 2007, you can simply enter the date by typing June 1, 2007 (or use any of several different date formats). Excel interprets your entry and stores the value 39234, which is the date serial number for that date.

Entering time values

When you work with times, you simply extend Excel’s date serial number system to include decimals. In other words, Excel works with times by using fractional days. For example, the date serial number for June 1, 2007, is 39234. Noon on June 1, 2007 (halfway through the day), is represented internally as 39234.5 because the time fraction is simply added to the date serial number to get the full date/time serial number.

Again, you normally don’t have to be concerned with these serial numbers (or fractional serial numbers, for times). Just enter the time into a cell in a recognized format.