Chapter 10

Working with Dates & Times

Microsoft Excel 2003

Date Serial Numbers

• To Excel, a date is just a number that represents the number of days since January 0, 1900.– A serial number of 1 represents the date

January 1, 1900.

• To view a date serial number, format the cell as a date using the Format Cells dialog box.

Date Formats

• Normally, you enter a date using any recognized date formats (see Table 10-1)

• Excel – converts your entry into the corresponding serial

number (which it uses for calculations) – applies the default date format to the cell so it

displays as an actual date rather than the serial number.

– Usually the default date format is your system’s short date format.

Time Serial Numbers

• To work with time values, extend the excel date serial number system to include decimals or fractional days.

• Noon at June 1, 2004 is represented by the serial number 38139.5

– One minute = 0.00069444– One second = 0.00001157– See Table 10-2 for other times of day serial

numbers.

Time Serial Numbers

• A time value without a date gets a date serial number of 0, which corresponds to the non-day January 0, 1900.0.81250000 = 7:30:00 PM

• If a time is entered that exceeds 24 hours, Excel increments the associated date for the time accordingly:27:00:00 = 1.12500000

Formatting Dates and Times

• You can format the cell to display – The date part only– The time part only– Both the date and the time parts

• Use the Format Cells dialog box to format dates and times to your desired format, or to create a custom format.

Problems with Dates

• Excel’s Leap Year Bug– Although the year 1900 was not a leap year, Excel

treats it as such.– Treats February 29, 1900 as a date

• Pre-1900 Dates– Must enter the dates into a cell as text.– Can’t perform any manipulation on dates entered

as text.– Can use the Add-in “Extended Date Functions”

included on your CD.• Inconsistent Date Entries

– Two digit year entries behave according to rules determined by your version of Excel. (see pg 197).

Date & Time Related Functions

• See Table 10-4 in your book for all of Excel’s date-related functions.

• See Table 10-5 in your book for all of Excel’s time-related functions.

Displaying the Current Date

• TODAY()– Updated whenever the worksheet is

calculated.

• To enter a date stamp, where the date will not change:– Ctrl+; (press the control key and the semi-

colon)

Displaying Any Date

• DATE()– Creates a date– 3 arguments: the year, the month, the day.

=DATE(A1, A2, A3)

=DATE(2006, 2, 30) results in the date March 2, 2006

Entering a Date (DATE)Entering the DATE function

The calculated result is displayed as both a serial value and as a formatted date value

The function expression is built as you enter arguments into the dialog box

Displaying Any Date

• DATEVALUE()– Converts a text string that looks like a date

into a date serial number.– 1 argument: a text string (must be

enclosed in quotes)

=DATEVALUE(“January 2, 2006”)

=DATEVALUE(“03/05/2006”) results in the date March 2, 2006

Extracting Date Values (Day, Month, and Year)

Entering the DAY, MONTH, and YEAR functions

The active cell, F12, is named “myDate” as shown in the Name box

Generating a Series of Dates

• Can use a formula instead of Excel’s AutoFill feature to create a series of dates.– Can change the first one and the others will

update automatically.

• Series of dates separated by 7 days=A1+7

• Series of dates separated by one month=DATE(YEAR(A1), MONTH(A1) + 1, DAY(A1)

• Series of dates separated by one year=DATE(YEAR(A1)+1, MONTH(A1), DAY(A1)

Converting a Non-Date String to a Date

• Use a formula that parses the text value.

• i.e. if A1 holds 20060101=DATE(LEFT(A1,4),MID(A1,5,2),RIGHT(A1,2))

Number of Days Between Two Dates

• Can use simple subtraction • Fence Post: EndDay – StartDay + 1• NETWORKDAYS function

– Calculates the number of workdays between two dates

– Uses optional range of cells that include holidays to exclude those dates as well

• WORKDAY function– Available only with the Analysis ToolPak.– Opposite of the NETWORKDAYS function.

Number of Years Between Two Dates

• Use the YEAR function to extract the year from each date.=YEAR(A1) – YEAR(A2)

• DATEDIF function– Calculates the number of days, months, or years

between two dates.– 3 arguments: (startdate, enddate, code that

represents the time unit of interest – see pg 205) – Must be entered manually – not available in

function dialog box.

Other Date Formulas

• Determining the Day of the Year (Julian Date)=A1-DATE(YEAR(A1), 1, 0)

• Determining the number of days remaining in the year after a particular date (in cell A1)=DATE(YEAR(A1), 12, 31) – A1

• To convert a particular day of the year (B1) to an actual date in a specified year (A1)=DATE( A1, 1, B1)

Other Date Formulas

• Determining the day of the week• Use the WEEKDAY function

=WEEKDAY(DATE(2006, 1, 1))

• Determining the date of the most recent Sunday=TODAY()-MOD(TODAY() -1, 7)

• Pg 207 – Determining the first day of the week after a date

• Pg 207 –Determining the nth occurrence of a day of the week in a month

• Pg 208-210 – Determining Holidays

Calculating the Day of the Week (WEEKDAY)

Displaying the weekday of a date value

Using a customer number format to display the weekday name

Calculating the Day of the Week (WEEKDAY)

Selecting the WEEKDAY function

Time-Related Functions

• NOW()– Displays the current date and time

• NOW() – TODAY()– Displays the current time without an

associated date

• Displaying any time where A1 holds the hour, B1 holds the minute, and C1 holds the seconds.=TIME(A1, B1, C1)

Calculating Dates (NOW and TODAY)Searching for a function “to display the current time”

Type your request for a function here and then click the Go command button to perform the search

The results of the function search appear in this list box. Click on a function to display its description below the list box .

Calculating Dates (NOW and TODAY)Displaying the function categories

Calculating Dates (NOW and TODAY)Function Arguments dialog box for the NOW function

The NOW() function is entered into cell B20 without any arguments.

Time-Related Functions

• TIMEVALUE()– Converts a text string that looks like a time

into a time serial number.

=TIMEVALUE(“5:45 AM”)

• Pg 214-215 – Summing times that exceed 24 hours

• Pg 217 – Converting from military time

• Pg 217-218 – Converting decimal hours, minutes, or seconds to a time.

Calculating Elapsed Time (TIME)

Time-Related Functions

• Pg 218 – Adding hours, minutes or seconds to a time

• Pg 219 – Rounding time values

• Pg 219-220 – Working with non-time-of-day values

Calculating Dates (NOW and TODAY)Formatting the display of the current time