Dates and Time Calculations

Dates Dates are stored as serial numbers in Excel Dates are stored as serial numbers in Excel What does the serial number represent? What does the serial number represent? Days are numbered from the beginning of the century Days are numbered from the beginning of the century The date serial number 1 corresponds to Janurary 1, 1900 The date serial number 1 corresponds to Janurary 1, 1900 To see the serial number, format the cell as a general number To see the serial number, format the cell as a general number Format the serial number of a date in whatever format you choose Format the serial number of a date in whatever format you choose 9/18/1981 9/18/ Sept Sept-81 Excel for the Macintosh used the 1904 date system Excel for the Macintosh used the 1904 date system Tools/Options allows you to select the 1904 system Tools/Options allows you to select the 1904 system Excel will automatically change from one system to another if you switch back and forth between systems Excel will automatically change from one system to another if you switch back and forth between systems

Dates, cont. Dates and times can be added, subtracted and included in other calculations Dates and times can be added, subtracted and included in other calculations You can enter formatted dates in formulas if you enclose them in quotes You can enter formatted dates in formulas if you enclose them in quotes ="5/12/2004"-"3/5/2004" would display a difference of 68 days ="5/12/2004"-"3/5/2004" would display a difference of 68 days Easier to use cell reference Easier to use cell reference

Time To enter time based on the 12 hour clock, type a space followed by a or p To enter time based on the 12 hour clock, type a space followed by a or p Without the AM or PM, Excel assumes a 24 hour clock Without the AM or PM, Excel assumes a 24 hour clock 3:00 is interpreted as 3:00 AM. 3:00 is interpreted as 3:00 AM.

Time Time is stored as decimal fractions Time is stored as decimal fractions Fractions of what? Fractions of what? 24 hrs * 60min./hr. * 60sec/min = 86,400 seconds in a 24 hour period 24 hrs * 60min./hr. * 60sec/min = 86,400 seconds in a 24 hour period At 12:00:01 AM just 1 second has past, At 12:00:01 AM just 1 second has past, 1/ 86,400 = = the fraction of the 24 hours which has past 1/ 86,400 = = the fraction of the 24 hours which has past Just as with serial dates, we can add and subtract time Just as with serial dates, we can add and subtract time You start work at 10:30:00 AM and leave at 12:30:00 PM for lunch You start work at 10:30:00 AM and leave at 12:30:00 PM for lunch You worked of 24 hours in the morning You worked of 24 hours in the morning You need to convert this to hours. You need to convert this to hours. Multiply *24 = 5 hours worked. Multiply *24 = 5 hours worked.

Useful Time functions There is a today and a now function There is a today and a now function Today() Today() 7/15/2006 7/15/2006 Now() Now() 7/15/ :11 7/15/ :11