Converting APR to monthly repayments
According to Wikipedia: The term annual percentage rate of charge (APR), corresponding sometimes to a nominal APR and sometimes to an effective APR (or EAPR), describes the interest rate for a whole year (annualized), rather than just a monthly fee/rate, as applied on a loan, mortgage loan, credit card, etc.
The plugin uses APR by default. If you want monthly or some other period of repayment you need to calculate the interest rate for the repayment period.
This is the formula:
r = (1 + i)1/n – 1
r = rate per period
i = annual interest eg: 8% is 0.08
n = number of payments in a year
Given 14.9% interest per year with monthly payments the sum is:
r = (1 + 0.149) 1/12 – 1
r = (1.149) 0.8333333 – 1
r = 1.01164 – 1
r = 0.01164
r = 1.164%
All very simple and can be used for weekly or even daily repayments.
Once you have the interest rate for the repayment period you can plug it into the amortization formula.