Excel 2007 Exponential Interpolation

Can I assume you already have an algorithm for doing linear interpolations?

Doing a simple exponential interpolation can be approached the same as a linear interpolation, if you will use a couple of helper columns. An exponential function is y=B*A^x which can be rewritten as ln(y)=ln(B)+x*ln(A) -- A linear function. If you add, in column D, a function =ln(C5) [copied down], now you can use your existing linear interpolation algorithm to on columns D and B to interpolate for ln(y). Then, obviously, add an =exp() function to get y.

Just looking at the graph of the data, you might consider a hyperbolic function y=B+A/X (still a linear function in 1/X). In this case, you would add a helper column to calculate 1/X [=1/B5 copied down], then apply your linear interpolation algorithm to y and 1/x.

If you do not have a working linear interpolation algorithm, let us know and we can help build the linear interpolation algorithm. As I've tried to show above, once you have the linear interpolation algorithm, many other interpolation schemes are essentially the same when the desired transformation is applied to the raw data.

You could just do a linear interpolation between points:

	B	C	D	E	F	G
4	Level	Claims		Level	Claims
5	50,000	13.999		65,000	10.496	F5: =PERCENTILE($C$5:$C$17, 1 - PERCENTRANK($B$5:$B$17, E5))
6	75,000	8.161
7	100,000	5.134
8	125,000	4.138
9	150,000	2.885
10	175,000	2.425
11	200,000	2.119
12	250,000	1.269
13	300,000	0.834
14	350,000	0.587
15	400,000	0.422
16	450,000	0.351
17	500,000	0.304

You're welcome.