# Method to calculate interpolation step value in Excel

Note

## 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.

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
``````

Note

You must type the reference to the step value in cell B1 as an absolute reference (with dollar signs).