# 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:

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`

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).

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