# Method to calculate interpolation step value in Excel

Applies to: Microsoft Office Excel 2007Excel 2010Excel 2016

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