The logic for PMT is "periodic" - it depends on the periodicity of the
interest rates and number of payments. The key is to make sure that the
two are kept coordinated, e.g., if a monthly payment is wanted, the
interest rate and number of payments need to be expressed as monthly
rate (APR/12) and months (yrs * 12). If semi-annual payments are
desired, the interest rate must be semiannual (APR/2) and number of
periods equal to twice the number of years.

For the formula, see Help's PV entry.


In article ,
"Dave C. in Hudson Valley, NY" <Dave C. in Hudson Valley,
wrote:

I need to recreate the PMT formula in a non-Excel equation format and looking
for some mathematics assistance. I also don't know the underlying logic
built into the PMT formula for compounding interest; is it montly/annual?

Thanks in advance for any assistance.