function round_decimals(original_number, decimals) {
  var result1 = original_number * Math.pow(10, decimals)
  var result2 = Math.round(result1)
  var result3 = result2 / Math.pow(10, decimals)
  return (result3)
}


function calculateGains(){

var TAX_RATE = "0.25";
var DAYS_PER_YEAR = 360;

var period = parseFloat(document.getElementById("period").value);
var amount = parseFloat(document.getElementById("amount").value);
var interestType = document.getElementById("interestType").options[document.getElementById("interestType").selectedIndex].value;

var interestRate = parseFloat(document.getElementById("interestRate").value);
interestRate = document.getElementById("interestRate").value;
interestRate = interestRate.replace(",",".");
if( interestRate.lastIndexOf("%") != -1) 
	interestRate = interestRate.substring(0,interestRate.lastIndexOf("%"));
interestRate = parseFloat(interestRate);

interestRate /= 100;


if (!isNaN(interestRate) && !isNaN(period) && !isNaN(amount) && (interestType == "TANB" || interestType == "TANL")){
   
   var interestValue = (period / DAYS_PER_YEAR) * interestRate * amount;
   if(interestType=="TANB"){
        interestValue *= (1 - TAX_RATE);
   }   

   interestValue = round_decimals(interestValue,2);

document.getElementById("interestValue").value = interestValue;
document.getElementById("finalAmount").value = amount + interestValue;
}else{
    alert("A Taxa de juro, Prazo e Montante a investir têm de ser valores numéricos.");
}
}