I would like to derive an equation that calculates the average interest payment x for an amortized mortgage loan in the first m months of the loan. Call the interest rate i and the principal p and the number of months n.
I understand the amortization equation shown in this wikipedia article and I understand how to calculate an amortization table by hand, but I do not no where to begin to derive the equation I am describing.
http://en.wikipedia.org/wiki/Amortization_calculator
I would greatly appreciate it if anyone could point me in the right direction. Thanks!