I need to be able to calculate the cumulative interest paid
on a loan the cumulative principal paid as well without using the
CUMIPMT and CUMPRINC functions in Excel.

I am linking data from an Excel spreadsheet to another program.
Regrettably, the program I am using doesn't support either the CUMIPMT
or CUMPRINC functions of Excel, so I need to be able to calculate this
data without using the built in Excel functions.

I have already tried adding worksheets to the workbook and calculating
each amortization schedule and then using the VLOOKUP function (which
the software does support) to get the data. While this worked, the
resulting workbook contained so many calculations that the result was
unusable.

Is this something you are trying to calculate after each monthly
payment or only at the end of the loan when it is paid in full?

I need to calculate for a given number of months as defined by one of
the cells in the spreadsheet.

A simple amortization table would calculate each month's interest and
pricipal. Totalling the colums is easy enough.

I need to be able to calculate the values without having to either
using the built in CUMIPMT and CUMPRINC functions or having to
calculate the entire amortization table.

Please let me know if any further clarification is needed.