Here is the mathematical formula:

n = -Log[1 - A*i / P] / Log[1 + i]

n = number of payments remaining
A = current balance
i = interest rate per payment period expressed as decimal
P = payment (principal + interest, not escrow, etc.)

Darryl

"eastcoastguyz" <eastcoastguyz[at]hotmail.com> wrote in message
news:1110796878.096659.18250[at]f14g2000cwb.googlegroups.com...
- quote -

In Excel use the NPER(Rate, pmt, pv,fv,type). This returns the number
of periods give the interest rate, payment and present value. payment
and interest rate should be per month and the answer will be months.

This is another reason I love my MS Money program, the calculators are all
built in. But if you don't have it, you might try going to this site and
downloading one of the spreadsheets and play with it. Good luck!

http://www.mtgprofessor.com/spreadsheets.htm

Kathy

"eastcoastguyz" <eastcoastguyz[at]hotmail.com> wrote in message
news:1110796878.096659.18250[at]f14g2000cwb.googlegroups.com...
- quote -

eastcoastguyz wrote:
- quote -

I don't know of any formula, but when I wanted to figure this out I set
up a simple spreadsheet like this:

Payment Amt.
----------- Month 1 | Month 2
----------- Prin. Balance | Prin. Bal.
| = Month1 Prin. Bal. + Month1 Interest
| - Month1 Payment Amt.
------------------- Interest due |Interest =
=((rate/12)*Prin. Bal.)|((rate/12)*Month2 Prin. Bal.
-------------------- Payment Amt. |Payment Amt.

Block and copy the monthly group of cells out to month 360, or
whatever, and then experiment with plugging in different Payment
Amounts and seeing when the Prin. Bal. goes to zero. Its not elegant,
but its quick and easy.

Andy

eastcoastguyz wrote:
- quote -

that's easier to track:

Just look at your amortization schedule, and add next months' principal
to the present month's payment. (This will be slightly more than your
present month's principal.) Then you've made your payment for the next
month as well.

In other words -- to January's payment, add february's principal. Then
in February, make March's payment and add April's principal to it, etc,
etc etc. That way you're making, in effect, two monthly payments every
month and you can easily see how much proncipal is left on the loan.

That's what I do. I actually add a few months principal to each month's
payment. It's affordable now, since I'm only 4 years into my 30 year
mortgage. As the principal portion of the payment increases, I will
eventually have to scale that back to just one extra month's principal
then to no extar principal. But I'll end up paying off my mortgage at
least 10 years early using this method.

Two caveats -- 1. Make sure that the mortgagee knows that the extra
payment is all principal, and 2. as you progress, paying the extra
months proncipal will get more expensive as the ratio between interest
and principal changes -- but that would also be the case with what
you're asking.

What I'm trying to do, is figure out the remaining length of a mortgage
if double principal payments are made.

Anyone know the formula or an excel spread sheet for this? Thanks!