Calculate compounded interest with periodic contributions

calculateCompoundInterest.js

const calculateCompoundInterest = (P, r, t, n, PMT, PMT_f, toFixed=2) => {
  /*
   * P = initial principle
   * r = interest rate (annual)
   * t = duration of invesment
   * n = compound events per year (1 = annual, 6 = semi-annual, 3 = quarterly, 12 = monthly, ...)
   * PMT = ongoing contibution amount
   * PMT_f = contributions per year (1 = annual, 6 = semi-annual, 3 = quarterly, 12 = monthly, ...)
   * --->
   * I = total investment
   * C = compounded interest
   * FV = future value
   */
  r /= 100; // 8 => 0.08 => 8%
  PMT *= parseFloat((PMT_f / n).toFixed(toFixed));
  P = parseFloat(P.toFixed(toFixed));

  const I = PMT * t + P;
  const FV = P * (1 + r / n) ** (n * t) + (PMT * (1 + r / n) ** (n * t) - PMT) / (r / n);

  return {
    totalInvestment: I,
    compoundedInterest: parseFloat((FV - I).toFixed(toFixed)),
    futureValue: parseFloat(FV.toFixed(toFixed)),
  };
};

// usage:
calculateCompoundInterest(10000, 5, 10, 12, 1000, 12);