Please Note: This article is written for users of the following Microsoft Excel versions: 2007, 2010, and 2013. If you are using an earlier version (Excel 2003 or earlier), this tip may not work for you. For a version of this tip written specifically for earlier versions of Excel, click here: Using the FORECAST Function.

Using the FORECAST Function

by Allen Wyatt
(last updated February 15, 2014)

1

The FORECAST function can be used whenever you have an existing set of data pairs (x-values and y-values) and you want to calculate an estimated y-value to a new x-value. Excel performs a linear regression based on the existing values and then inserts the x-values into the expression for the regression which gives you an y-value. The new x-value can have any value and is not restricted to be larger than the existing x-values.

The FORECAST function uses the following syntax:

=FORECAST(X, Yrange, Xrange)

In this usage, X is the X value for which you want FORECAST to return a Y value. The Yrange and Xrange parameters are sets of know Y and X values.

As and example, let's say that you are going on a diet, and you decide to keep track of your weight each day. Every day you enter the date into column A and the weight for that day in column B. After getting about 10 days or so of measurements, you can use these data pairs to forecast when you will hit your target weight. If your target weight is 160 lbs., you could use the following formula:

=FORECAST(160, A2:A11, B2:B11)

The result is the anticipated date when you will reach the target weight. (This is, admittedly, a very simplistic example. Unless your metabolism is abnormal, your weight loss won't follow a straight line; it will likely decrease over time.)

Excel calculates the "trend line" (using linear regression) of the points in A2:B11 (i.e., it assumes there is a linear relationship between the dates and the weights. (This trend line is the same as you would get from plotting the data pairs and adding a trend line to the chart.)

The suitability of the FORECAST function to what you are trying to accomplish is directly tied the characteristics of the data you are working with. Suppose, for example, that you have data that increases by 5% per month over time, and you want to forecast how that data is likely to progress in the future. In such a situation you wouldn't want to use FORECAST because it works on linear data, and a 5% increase per month is not linear—it is exponential. Fitting a linear trend to an exponential data set results in an underestimation when you forecast the data. Instead you should use the GROWTH function as it is better suited for your data.

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (9176) applies to Microsoft Excel 2007, 2010, and 2013. You can find a version of this tip for the older menu interface of Excel here: Using the FORECAST Function.

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

Converting Mainframe Date Formats

Different industries and different computer systems specify dates in all sorts of strange ways. If you need to convert a date ...

Discover More

Deleting Paragraph Borders

Got a document that has a border around some paragraphs? Here's how you can get rid of the border using the tools on the Home ...

Discover More

Making a Named Range Non-Scrollable

Excel provides a few ways that you can freeze or split what you see in your worksheet. The appropriateness of these tools to ...

Discover More

Create Custom Apps with VBA! Discover how to extend the capabilities of Office 2013 (Word, Excel, PowerPoint, Outlook, and Access) with VBA programming, using it for writing macros, automating Office applications, and creating custom applications. Check out Mastering VBA for Office 2013 today!

More ExcelTips (ribbon)

Using the WEEKNUM Function

Need to know which week of the year a particular date falls within? Excel provides the WEEKNUM function so you can easily ...

Discover More

Converting to Hexadecimal

Excel allows you to easily convert values from decimal to other numbering systems, such as hexadecimal. This tip explains how ...

Discover More

Rounding to the Nearest $50

When preparing financial reports, it may make your data easier to understand if you round it to the nearest multiple, such as ...

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

If you would like to add an image to your comment (not an avatar, but an image to help in making the point of your comment), include the characters [{fig}] in your comment text. You’ll be prompted to upload your image when you submit the comment. Maximum image size is 6Mpixels. Images larger than 600px wide or 1000px tall will be reduced. Up to three images may be included in a comment. All images are subject to review. Commenting privileges may be curtailed if inappropriate images are posted.

What is 7 - 1?

2014-07-10 01:59:07

Dean Robinson

Hi Allen,
Thanks for this tip. I am using the forecast function but find it confusing as to why it does not seem to work in reverse. For example, if I use the case you have provided above to forecast the date which you hit 160 lbs - and I then feed that date into the Forecast function switching the "known x's" and "known y's" I was thinking you would get the answer 160 lbs. However, this does not seem to be the case. Any ideas?


This Site

Got a version of Excel that uses the ribbon interface (Excel 2007 or later)? This site is for you! If you use an earlier version of Excel, visit our ExcelTips site focusing on the menu interface.

Newest Tips
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.