A useful formula is $P=R\cdot \frac{1-(1+i)^{-n}}{i}$, where $P$ is the size of the loan (principal); $i$ is the interest rate per period (not the annual rate); and $n$ is the number of interest periods over the life of the loan.
A useful formula is $P=R\cdot \frac{1-(1+i)^{-n}}{i}$, where $P$ is the size of the loan (principal); $i$ is the interest rate per period (not the annual rate); and $n$ is the number of interest periods over the life of the loan.