calc.js

// Compound interest for principal
// CIfP = P(1+r/n)^nt

// Future value of a series:
// PMT * (((1 + r/n)^nt - 1) / (r/n)) * (1+r/n)

// Total = [ Compound interest for principal ] + [ Future value of a series ]
// Total = [ P(1+r/n)^nt ] + [ PMT * (((1 + r/n)^nt - 1) / (r/n)) ]

// CIfP = the future value of the investment/loan, including interest
// P = the principal investment amount (the initial deposit)
// r = the annual interest rate (decimal)
// n = the number of times that interest is compounded per year AND additional payment frequency
// t = the number of years the money is invested
// PMT = the monthly payment

const P = 5000
const r = 0.10
const n = 12
const t = 10
const PMT = 1000

const options =
`Initial Capital: ${P}
Interest Rate: ${r}% (decimal)
Years: ${t}
Monthly payment: ${PMT}
`

let CIfP = (P * Math.pow((1 + r/n), n*t)).toFixed(2)

let FVoS = (PMT * ( ( (Math.pow((1 + r/n), n*t) - 1) ) / (r/n) * (1+r/n)  )).toFixed(2)

let Balance = (parseFloat(CIfP) + parseFloat(FVoS)).toFixed(2)

let RowInvestment = n * PMT * t + P
let Gain = (Balance - RowInvestment).toFixed(2)

console.log(options)
console.log(`Balance: ${Balance}, \nInvestment: ${RowInvestment}\nTotal Interest: ${Gain}`);
console.log(`Monthly: ${((Balance * 0.1)/12).toFixed(2)}`);