>What I am trying to calculate is the interest rate if a person pays there mortgage every other week which gives 1 extra payment. I want to know the equivalent. So I do know the number of payments. I calculate that first to show a person the difference between the original loan and paying it biweekly. I will look at the payment calculation and see if that helps.
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>Thanks everyone for your input...

Dunno, but I'd say that the intrest rate won't change. If a person pays weekly instead of biweekly, then the total intrest paid will be less - as will the payment per period

Total intrest paid = pmt * number_of_payments - pv