With your posted data list in A1:B27

and...
D1: (the "Y" value to find in B2:B27......eg 3500)

This formula (in sections for readability) returns
the interpolated "X" value from A2:A27:

E1: =FORECAST(D1,OFFSET(A2:A27,MATCH(D1,A2:A27,1)+1,,2 ,1),
OFFSET(B2:B27,MATCH(D1,A2:A27,1)+1,,2,1))

Using that example, the formula returns: 147000

-------------------------------
Or....to interpolate the other column
D1: (the "X" value to find in A2:A27......eg 147000)

This formula (in sections for readability) returns
the interpolated "Y" value from A2:A27:

E1: =FORECAST(D1,OFFSET(B2:B27,MATCH(D1,A2:A27,1)+1,,2 ,1),
OFFSET(A2:A27,MATCH(D1,A2:A27,1)+1,,2,1))

In that case, the formula returns: 3500

Is that something you can work with?
--------------------------

Regards,

Ron
Microsoft MVP (Excel)
(XL2003, Win XP)

"proinwv" wrote in message
...
All,

My data is in two columns of X and Y but is not linear. (See below)

I tried the suggestion for FORECAST but it will not return the correct
value
becasue of the non-lineararity.

I tried PERCENTILE, but it is not recognized. Possibly because of my
version
being older (Excel 2000)?

Is there another method? My data is as shown below. Charting it shows the
non-lineararity to be significant.

X Y
2,500 60
4,200 100
21,000 500
42,000 1,000
84,000 2,000
126,000 3,000
168,000 4,000
210,000 5,000
420,000 10,000
630,000 15,000
840,000 20,000
1,050,000 24,000
1,260,000 28,000
1,470,000 31,000
1,680,000 34,000
1,890,000 37,000
2,100,000 40,000
2,520,000 44,000
2,940,000 48,000
3,360,000 52,000
3,780,000 56,000
4,200,000 60,000
5,040,000 68,000
5,880,000 75,000
6,720,000 82,000
7,560,000 90,000