I am building a javascript calculator for compounding interest monthly my problem is how I could deduct the tax at every end of the year or every 12 months. for example: If someone selected 65 months it will then calculate the compound interest monthly and subtract tax by the end on the month so you have to subtract it on 12th, 24th, 36th, 48th, 60th and the last 5 months

   var compound = document.getElementById('amount').value;
   var interest = document.getElementById('interest').value;
   var interest = document.getElementById('taxrate').value; //input for tax rate
   var nummonth = document.getElementById('months').value;
   interest = 1 + (interest/100); //convert to dec
   var tableHTML = '';
  
    if(!compound || !interest || !nummonth || !taxrate){
      alert('Please fill all boxes');
      return;
    }
      //What should I use or do for displaying or calculating the amount with taxrate in every 12th iteration 
      for (i = 0; i <= nummonth; i++) {
        var res = compound * (Math.pow(interest, i));
        res = res.toFixed(0);
      
      var interestgained = (+res * interest)-res;
      interestgained = interestgained.toFixed(0);

      var powint = compound * (Math.pow(interest, i));
   
      powint = powint.toFixed(0);
      
      var tr = powint - compound;

      var ointerest = (interest - 1)*100;
      ointerest = ointerest.toFixed(0);

   
        tableHTML = tableHTML + "<tr><td>Compound: " + i + "</td><td> " + "$"+res + "</td><td> " + ointerest + "%"+"</td><td> " + "$"+interestgained + "</td><td>"+ "$"+powint +"</td></tr>";
      }
    document.getElementById("totalInterest").innerHTML = "$"+tr;
    document.getElementById("totalPayment").innerHTML = "$"+powint;
    document.getElementById("totalwithtax").innerHTML = "$"+tax;// I want to display here
      document.getElementById("tdisplay").innerHTML = "<thead><tr><th>Month</th><th>Amount</th><th>Interest</th><th>Total Return</th><th>Total Amount</th></tr> </thead>"+ tableHTML;