Compound interest where interest is calculated daily, but credited monthly.

Iterative compound interest calculator.js

var finalAmount = (function() {
  var initialPounds = 40000;
  var denominationOfYearUponWhichInterestCalculated = 365;
  var denominationsAfterWhichInterestCredited = Math.floor(denominationOfYearUponWhichInterestCalculated/12);
  var annnualInterestCoefficient = 1.05;
  var denominationInterestCoefficient = Math.pow(annnualInterestCoefficient, 1/denominationOfYearUponWhichInterestCalculated);
  var yearsSimulated = 5;
  var amountSpentPerMonth = 500;
  var amountSpentPerYear = amountSpentPerMonth*12;
  var amountSpentPerDenomination = amountSpentPerYear/denominationOfYearUponWhichInterestCalculated;
  var currentAmount = initialPounds;
  var i;
  var j;
  var denominationsPassed = 0;
  var interestWaitingToBeCredited = 0;
  for(i=0; i<yearsSimulated; i++) {
    console.log(currentAmount.toFixed(2));
    for(j = 0; j<denominationOfYearUponWhichInterestCalculated; j++) {
      // console.log(currentAmount.toFixed(2));
      var interestEarnedDuringThisDenomination = (currentAmount+interestWaitingToBeCredited)*denominationInterestCoefficient-(currentAmount+interestWaitingToBeCredited);
      interestWaitingToBeCredited += interestEarnedDuringThisDenomination;
      currentAmount -= amountSpentPerDenomination;

      denominationsPassed++;
      if (denominationsPassed%denominationsAfterWhichInterestCredited == 0) {
        currentAmount += interestWaitingToBeCredited;
        interestWaitingToBeCredited = 0;
      }
    }
  }
  return currentAmount;
})();
console.log(finalAmount.toFixed(2));