Method to calculate interpolation step value in Excel

Summary

The following Microsoft Excel formula performs linear interpolation by calculating the interpolation step value:

=(end-start)/(ROW(end)-ROW(start))

where end is the cell address of the larger number, and start is the cell address of the smaller number.

Interpolation is a method used to determine a present or future value factor when the exact factor does not appear in either a present or future value table. Interpolation assumes that the change between two values is linear and that the margin of error is insignificant.

More Information

To create a sample linear interpolation formula, follow these steps:

1. Type the following values in a worksheet:

   A1: 9        B1: =(A7-A1)/(ROW(A7)-ROW(A1))
   A2: =A1+$B$1
   A3:
   A4:
   A5:
   A6:
   A7: 11
   

2. Select cells A2:A6. On the Edit menu, point to Fill, and then click Down. The formula is filled down, and the following values are displayed in cells A2:A6:

   A2: 9.33333
   A3: 9.66667
   A4: 10.
   A5: 10.33333
   A6: 10.66667