Calculating future value with compound interest with JavaScript

Question

I\'m trying to work on a script where the user inserts a monthly income and gets the future value with compound interest after 30 years. As it is now, I\'ve assigned some values

Answer 1

The Math.pow is unnecessary, since you are calculating and incrementing futureValue month by month. Simply multiply by 1 + monthlyRate. You also want to add the current value of the investment to the new investment before multiplying:

for ( i = 1; i <= months; i++ ) {
   futureValue = (futureValue + investment) * (1 + monthlyRate);
}

Alternatively, you can also calculate this in one go with the following formula:

futureValue = investment * (Math.pow(1 + monthlyRate, months) - 1) / monthlyRate;