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 for testing purposes. 

```
// Future Value
var investment = 800;
var annualRate = 2;
var monthlyRate = annualRate / 12 / 100;
var years = 30;
var months = years * 12;
var futureValue = 0;

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

```

Problem is, I'm actually building this from an Excel spreadsheet that's using the built-in FV() formula and when cross checking, my results are totally off... Any idea what I'm doing wrong since I'm not into finance math at all. Thanks in advance.