Don't know what's standard practice in your location, but I'd think it
depends on how the interest is calculated during the extra 15 days. For
instance, if the interest is compounded daily (and based on 30 days per
month), then:

=PMT(Rate/360, Months*30, FV(Rate/360,15,0,Prin))*30

OTOH, if compounding is monthly, perhaps:


=PMT(Rate/12, Months, FV(Rate/12,0.5,0,Prin))


In article ,
mikeb wrote:

I am trying to use payment function and would like the first payment to be in
45 days with the remaining payments 30 days each month thereafter.