Interpolating data points in Excel

Question

I\'m sure this is the kind of problem other have solved many times before.

A group of people are going to do measurements (Home energy usage to be exact). All of them wi

Answer 1

I came across this and was reluctant to use an add-in because it makes it tough to share the sheet with people who don't have the add-in installed.

My officemate designed a clean formula that is relatively compact (at the expensive of using a bit of magic).

Things to note:

• The formula works by:

  • using the MATCH function to find the row in the inputs range just before the value being searched for (e.g. 3 is the value just before 3.5)
  • using OFFSETs to select the square of that line and the next (in light purple)
  • using FORECAST to build a linear interpolation using just those two points, and getting the result

• This formula cannot do extrapolations; make sure that your search value is between the endpoints (I do this in the example below by having extreme values).

Not sure if this is too complicated for folks; but it had the benefit of being very portable (and simpler than many alternate solutions).

If you want to copy-paste the formula, it is:

=FORECAST(F3,OFFSET(inputs,MATCH(F3,inputs)-1,1,2,1),OFFSET(inputs,MATCH(F3,inputs)-1,0,2,1

(inputs being a named range)