How to Build a Personal Loan Calculator

function calculatePersonalLoan(amount, apr, months, originationFee = 0) {
  const feeAmount = amount * (originationFee / 100);
  const fundedAmount = amount - feeAmount; // What you actually receive
  const monthlyRate = apr / 100 / 12;

  const payment = amount *
    (monthlyRate * Math.pow(1 + monthlyRate, months)) /
    (Math.pow(1 + monthlyRate, months) - 1);

  const totalInterest = (payment * months) - amount;

  return {
    loanAmount: amount,
    fundedAmount,
    originationFee: feeAmount,
    monthlyPayment: payment,
    totalInterest,
    totalCost: payment * months
  };
}