Linear Interpolation In Excel

There are many ways to perform linear interpolation (or extrapolation) in Excel. The examples below assume that you know at least two points (x₁,y₁) and (x₂,y₂) and want to solve for y given x based on the equation for a line: y=mx+b, where m is the slope and b is the y-intercept.



1. Using the Point-Slope formula, where the slope is (y₂-y₁)/(x₂-x₁):

y=y1+(x-x1)*(y2-y1)/(x2-x1)
=B2+(B5-A2)*(B3-B2)/(A3-A2)

2. Using the SLOPE and INTERCEPT functions to solve for m and b:

y=SLOPE(y's,x's)*x+INTERCEPT(y's,x's)
=SLOPE(B2:B3,A2:A3)*B5+INTERCEPT(B2:B3,A2:A3)

3. The TREND function uses linear regression to solve for y if you have two or more points. This is also a way to estimate y from a linear fit of many points.

y=TREND(y's,x's,x,TRUE)
=TREND(B2:B3,A2:A3,B5,TRUE)