function formatCommas(str) {
  var re = /(-?\d+)(\d{3})/;
  while (re.test(str))
  {
    str = str.replace(re, "$1 $2");
  }
  return str;
}

function CreditCalc() {
  var credit_result = document.getElementById('credit_result');

  var amount = document.getElementById('credit_amount').value;
  var percent = document.getElementById('credit_percent').value / 100;
  var time = document.getElementById('credit_time').value * 12;

  var pay = Math.round( (amount * percent / 12) / (1 - 1 / Math.pow(1 + (percent / 12), time)) );
  if (pay)
  {
    var pay_str = formatCommas(pay.toString());
    credit_result.innerHTML = 'Ежемесячный платеж: <b class="color_green">' + pay_str + '</b>';
  }
  else
  {
    credit_result.innerHTML = '';
  }
}