How to interpolate data in Excel?

[Yossarian]

I'm trying to write a formula to interpolate and I can't figure it out.

As a simple example, I have the following in Excel (each in its own cell of course):

64 2400
73 2500
77 2550

I want to be able to enter 75 in another cell, and come back with a result of 2525. Any tips?

 

[WannaFly]

If your second column is a formula, you can use solver to find the number, i believe.

 

[Yossarian]

I wish it were, but it's just numbers from a chart of aircraft performance.

 

[joepa99]

you can use the TREND formula. You may have decimal places, but that is the best formula to use.

 

[kmmatney]

If you're just doing linear interpolation, then type in the equation youself using the good old equation for a line:

y2 - y1 = Slope * (X2 - X1)

In this case you'd have:

Slope = (2550 - 2500)/(77 - 73) = 12.5

then
Y(New) - Y1 = SLope * (X(new) - X1)

Y(75) = 12.5 * (75 - 73) + 2500 = 2525

Just replace the hard-coded numbers with cell references.