# Method to calculate interpolation step value in Excel

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## 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).

## Properties

Article ID: 214096 - Last Review: September 18, 2011 - Revision: 5.0
##### APPLIES TO
• Microsoft Office Excel 2007
• Microsoft Excel 2002 Standard Edition
• Microsoft Excel 2000 Standard Edition
• Microsoft Excel 2010
##### Keywords:
kbhowto kbinfo KB214096