"Marc" wrote:
In cell L57 I have the annual interest rate, in M57 the
numbers of years for the loan and K57 is the principal.

"Marc" wrote later:
This is my formula now
=PMT((L57/M57*12)%,(M57*12),-K57)

You formula is completely wrong. The correct formula for
the terms stated earlier is simply:

=PMT(L57/12, M57*12, -K57)

(This assumes that L57 contain "8%" or "0.08", without quotes.)

That results in $11,130.69.

but it returns $137,117.87. If you divide this by 12 you get
$11,426.49.

Pure coincidence, as near as I can tell. Taken the PMT() result
and dividing by 12 makes no sense to me.

If I use the loan calculator at this site
http://www.tcalc.com/tvwww.dll?CalcLoan I get 14,480.12.

It might help if you specify the parameters and options you enter.

I get $11,130.69 -- same as PMT() -- from that calculator when
I enter the following:

Loan start date: 05-06-2006
First payment date: 06-06-2006
Loan amount: $714,136.63
Number of payments: 84
Payment period: Monthly
Interest rate: 8%
Compounding period: Monthly
Loan type: Fixed Rate

All other fields are "don't cares". I left them as-is.

If you entered different values, you are using different loan
terms. Which is right depends on the actual loan terms.