From: Ronald Raygun 
Subject: Re: mortage calc
Newsgroups: uk.finance
Date: Tue, 10 Jan 2006 15:46:44 GMT

Jenson wrote:

> Anyone know of an on-line mortage calculator which will show me a monthly
> breakdown of amount owed?

Don't know, but if you use one of the ones which tell you what
the monthly payment P is (given the amount borrowed A, the number
of months N in the term, and the monthly interest rate f-1), then

the amount owed when there are M months of the term still remaining is

P * (1 - f^-M) / (f-1)

Better still, don't bother with finding P on-line, or even off-line,
the answer is simply:

A * (1 - f^-M) / (1 - f^-N)

Notice in particular how for M=N (i.e. with the full term still to
run) this works out at A, as it should, and for M=0 (i.e. at term
end) it works out at 0, as it should.