"Propertyman" wrote:
I wish to determine the impact of paying my motgage say
weeky or fortnightly by dividing my monthly repayment
accordingly and remitting my payments more frequently.

There are two issues he Excel formulation, and the pros
and cons of accelerated payment schedules (weekly, biweekly
and semimonthly).

I will attempt to help with the Excel formulation question
because I am not personally familiar with the mechanics of
accelerated payment schedules, and there is some ambiguity
or dubiousness in the explanations that I find on the web.

But I do suggest that you do a Google search for "accelerated
mortgage payments" or "biweekly mortgage payments" (without
quotes) and read some of the items. This time, be sure to go
beyond the first page of Google results. Some of them bring
up points beyond the numerical comparison, as well as a
heads-up about some business practices that you might want
to question lenders about.