how do I calculate a monthly payment based on a variable rate?

[Guest]

I have to calculate a monthly payment based on avariable interest rate. What
is the formula I use, ex. variable rate in is A6, loan term B6, and payment
C6?

 

[Guest]

Do you mean the initial loan amount is in C6?
Until the rate changes, you have to base the payments on the current rate
and term. =pmt(a6/12,b6*12,-c6). This assumes your rate and term are annual
and your payments are monthly. Once the rate changes, you'd reestablish the
payment based on the new rate, the remaining term and the remaining loan
balance.