I got undefined in the first iteration any comments is helpful to me thanks in advance

for (i = 0; i <= nummonth; i++) {
    var res = compound * (Math.pow(interest, i));
    res = res.toFixed(0);
  var tableHTML;
  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>";
  }