mortgage calculation script

mg.js

const loan = 100000
const interestRate = 2.9 / 100
const monthlyInterestRate = (interestRate / 12)
const numOfPayments = 360
const interestRateExponent = Math.pow((monthlyInterestRate + 1), numOfPayments)

/**
 * M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
 *   */
const payment = loan * (
  monthlyInterestRate * interestRateExponent
) / (
  interestRateExponent - 1
)
const totalToPay = (payment * numOfPayments)
const totalInterestToPay = (totalToPay - loan)

let totalPaid = 0
let overPaid = 0

const totalInterestIncrements = (numOfPayments * (1 + numOfPayments)) / 2
const interestPerIncrement = totalInterestToPay / totalInterestIncrements

for (let paymentNum = 0; paymentNum < numOfPayments; paymentNum++) {
  const remainingPayments = (numOfPayments - (paymentNum + 1))
  const interestInPayment = (remainingPayments * interestPerIncrement)
  totalPaid += payment
  overPaid += interestInPayment
  console.log(
    `${paymentNum},` +
    `${payment.toFixed(2)},` +
    `${interestInPayment.toFixed(2)},` +
    `${overPaid.toFixed(2)}`
  )
}

console.log({
  interestPerIncrement,
  totalInterestIncrements,
  totalInterestToPay,
  totalPaid,
})