loan-total-cost.js

// totalCostOverMonths returns the total cost of an amortizing loan given a fixed APR.
const totalCostOverMonths = (
  p, /* The principal borrowed */
  r, /* The APR / 1200 if APR is taken as a percentage; e.g., with APR of 9%, r = 9/1200 = 0.0075 */
  m  /* The number of months the mortgage is held for; the number of payments */
) => p * r * m / (1 - Math.pow(1 + r, -m)) - p;