Understanding How Excel Records Dates and Times
Calculating with Date and Time
Working with Date and Time Functions
YOU can use date and time values to stamp documents and to perform date and time arithmetic. Creating a production schedule or a monthly billing system is relatively easy with Microsoft Excel 2010. Although Excel 2010 uses numeric values to count each nanosecond, starting from the beginning of the twentieth century, you can use formatting to display those numbers in whatever form you want.
Excel assigns serial values to days, hours, minutes, and seconds, which makes it possible for you to perform sophisticated date and time arithmetic. The basic unit of time in Excel is the day. Each day is represented by a serial date value. The base date, represented by the serial value 1, is Sunday, January 1, 1900. When you enter a date in your worksheet, Excel records the date as a serial value that represents the number of days between the base date and the specified date. For example, Excel represents the date January 1, 2008, by the serial value 39,448, representing the number of days between the base date—January 1, 1900—and January 1, 2008.
The time of day is a decimal value that represents the portion of a day that has passed since the day began—midnight—to the specified time. Therefore, Excel represents noon by the value 0.5 because the difference between midnight and noon is exactly half a day. Excel represents the time/date combination 12:59:54 PM, October 6, 2006, by the serial value 38996.54159 because October 6, 2006, is day 38,996 (counting January 1, 1900, as day 1), and the interval between midnight and 12:59:54 PM amounts to .54159 of a whole day.