
You will now be able to graph columns B:D to show how well the prediction matches the historical actuals.Īdditional Details: When the data along one axis of your data contains dates, it is best to delete the heading in the upper-left corner of your data set before creating the chart.

It turns out that Excel really wants to return two numbers from the function.

The first time you do this, you might wonder how the number 204.81 could describe a line. Entering the formula the wrong way returns a single answer of 204.8133. If you select a single cell and enter =LINEST(C2:C35), it will return a single number, which is of no help. Instead of returning one number, it actually returns two (or more) numbers as the result. This is just my wild guess Excel can calculate the number exactly. In this case, the value for b would be 10,000, and the value for m would be 400.

If you were to look at the data, you might guess that the prediction for a given month is $10,000 + Month number x $400. In this example, y is the revenue for the month, m is the slope of the line, x is the month number, and b is the y-intercept. You might remember from math class that a trendline is represented by this formula: y = mx + b Excel offers a function called LINEST that will calculate the formula for the trendline. Strategy: You can use the least-squares method to fit the sales data to a trendline. Problem: I have monthly historical sales data.
