Calculating Values based on dates and indexes!

A sample file would help but for the sake of demo. let's assume the following:

Initial Value: A1 (numeric value)
Beg Date: A2 (date value - 1st of month)
End Date: A3 (date value - 1st of month)

Index Table C1:Dx
x is last row - unknown - for arguments sake let's make this 13
Column C contains Months as date values (1st of month)
Column D contains the Index % values


Result to go in A4 based on A1:A3 in related to C1:D13

A4: =A1*(1+SUM(INDEX(D1:D13;MATCH(A2;C1:C13)):INDEX(D1:D13;MATCH(A3;C1:C13))))

not quite sure where you get the 1.74% - I get 1.43%

DO,

I think it is interest OVER interest. In dutch we call in "samengestelde" interest. Don't know how it is called in english but this example will clarify.

For the same interest (7%) for 5 years:
DO: 1000 * 1+5*0.07
ME: 1000 * (1+0.07)^5

That would make your solution:
=A1*(PRODUCT(1+INDEX(D1:D13,MATCH(A2,C1:C13)):INDEX(D1:D13,MATCH(A3,C1:C13))))

CSE (array)

I might be wrong.