do I have to manually change PER to amortize a loan out 40 years?

I'm amortizing 40-year notes using PPMT to calculate the principal payment.
For each new monthly payment I have to manually change PER in the formula.
I'm using Excel 2003. Is there any easier way to do this?-

If you're creating a payment (amortization) table, you can have a column of
numbers for the payments (say 1 through 180 for a 15-year mortgage); then
you can set PER equal to the cell address. NPER will be a constant, which
you can enter in a cell and assign an absolute address (like $a$4).

Chuck

If you're creating a payment (amortization) table, you can have a column of
numbers for the payments (say 1 through 180 for a 15-year mortgage); then
you can set PER equal to the cell address. NPER will be a constant, which
you can enter in a cell and assign an absolute address (like $a$4).

Chuck