Please Note: This article is written for users of the following Microsoft Excel versions: 97, 2000, 2002, and 2003. If you are using a later version (Excel 2007 or later), this tip may not work for you. For a version of this tip written specifically for later versions of Excel, click here: Calculating the Last Day in a Week Number.

Calculating the Last Day in a Week Number

by Allen Wyatt
(last updated September 16, 2013)

You probably know that you can use the WEEKNUM function to return the week number in a year for a given date. What if you want to do the reverse—to determine the last day of a particular week if all you have is the week number within the year? For instance, if you were to specify week 37, you would like to figure out the date of the last day in that particular week.

There is no built-in function to figure out the desired date, but there are a number of ways that you can approach the problem and figure it out. In these examples we will assume that the year is in cell A1 and the desired week number is in cell B1.

The first approach is to calculate the first day of the desired year, add seven days for each of the weeks, and then subtract the weekday number for the first day of the year.

=DATE(A1,1,1)+B1*7-WEEKDAY(DATE(A1,1,1))

This formula returns a date that always represents the last day of the week, if the week ends on a Saturday. If you want the week to end on a different day of the week then the formula becomes more complex. If you want the week to end on a Sunday, then you simply need to add 1 to the formula:

=DATE(A1,1,1)+B1*7-WEEKDAY(DATE(A1,1,1))+1

Applying this same logic, you might think that you could figure out weeks ending on Friday by simply subtracting 1 from the formula. This is not the case since you are using the beginning of the year as your base. If you subtract 1, you run into the problem where January 1 of whatever year is a Saturday; if you subtract 1 you don't end up with the first Friday of the year but instead end up with December 31 of the previous year. To calculate for weeks ending on Friday you need a much more complex formula:

=DATE(A1,1,6-WEEKDAY(DATE(A1,1,1))+
((6-WEEKDAY(DATE(A1,1,1))<0)*7)+1)+((B1-1)*7)

Since some years have 52 weeks and some have 53—again depending on whether weeks end on Friday, Saturday, or Sunday—it is a good idea to modify the formulas so that they check to see if the date being returned is within the same year that you are analyzing. If you don't check this, then the formulas provided thus far will happily return dates for week 73, week 89, or week 123 of any given year—they simply adjust the date into the appropriate future year.

Here is the formula for weeks ending in Friday:

=IF(YEAR(DATE(A1,1,6-WEEKDAY(DATE(A1,1,1))+
((6-WEEKDAY(DATE(A1,1,1))<0)*7)+1)+((B1-1)*7))=A1,
DATE(A1,1,6-WEEKDAY(DATE(A1,1,1))+((6-WEEKDAY(DATE(
A1,1,1))<0)*7)+1)+((B1-1)*7),"")

If the date calculated is not in the same year as what is specified in cell A1, then the formula returns nothing. Here is the formula for weeks ending in Saturday:

=IF(YEAR(DATE(A1,1,1)+B1*7-WEEKDAY(DATE(A1,1,1)))=A1,
DATE(A1,1,1)+B1*7-WEEKDAY(DATE(A1,1,1)),"")

Finally, here is the formula for weeks ending in Sunday:

=IF(YEAR(DATE(A1,1,1)+B1*7-WEEKDAY(DATE(A1,1,1))+1)=A1,
DATE(A1,1,1)+B1*7-WEEKDAY(DATE(A1,1,1))+1,"")

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (6750) applies to Microsoft Excel 97, 2000, 2002, and 2003. You can find a version of this tip for the ribbon interface of Excel (Excel 2007 and later) here: Calculating the Last Day in a Week Number.

Author Bio

Allen Wyatt

With more than 50 non-fiction books and numerous magazine articles to his credit, Allen Wyatt is an internationally recognized author. He  is president of Sharon Parq Associates, a computer and publishing services company. ...

MORE FROM ALLEN

Understanding Date and Time Formatting Codes

Want to apply a custom format to your dates and times? To do it effectively you need to understand the custom formatting ...

Discover More

Displaying File Extensions

File extensions help both you and Windows understand how to work with a particular file. By default these extensions are not ...

Discover More

Selecting an Entire Section

Documents can be subdivided into sections, with each of them formatted differently. If you want to select all the text in a ...

Discover More

Save Time and Supercharge Excel! Automate virtually any routine task and save yourself hours, days, maybe even weeks. Then, learn how to make Excel do things you thought were simply impossible! Mastering advanced Excel macros has never been easier. Check out Excel 2010 VBA and Macros today!

MORE EXCELTIPS (MENU)

Unique Military Date Format

Some industries (such as the military) have special formatting that they use to represent dates. Here is one such format and ...

Discover More

Converting Coded Dates into Real Dates

Sometimes the format in which you receive data is not the same format that would be optimal for Excel. For instance, you ...

Discover More

Ages in Years and Months

Calculating an age is a common task when working with dates. If you want to figure out the number of years and months between ...

Discover More
Subscribe

FREE SERVICE: Get tips like this every week in ExcelTips, a free productivity newsletter. Enter your address and click "Subscribe."

View most recent newsletter.

Comments for this tip:

There are currently no comments for this tip. (Be the first to leave your comment—just use the simple form above!)

This Site

Got a version of Excel that uses the menu interface (Excel 97, Excel 2000, Excel 2002, or Excel 2003)? This site is for you! If you use a later version of Excel, visit our ExcelTips site focusing on the ribbon interface.

Subscribe

FREE SERVICE: Get tips like this every week in ExcelTips, a free productivity newsletter. Enter your address and click "Subscribe."

(Your e-mail address is not shared with anyone, ever.)

View the most recent newsletter.

Links and Sharing
Share