$ = function(el) {
  if(document.getElementById(el)) return document.getElementById(el);
}

var rates = new Array(
  { l: 5, u: 1000, r: 6.5, i: '6.5%', a: '93.21%' },
  { l: 1000, u: 5000, r: 5.0, i: '5.0%', a: '69%' },
  { l: 5000, u: 10000, r: 4.0, i: '4.0%', a: '53.76%' },
  { l: 10000, u: 20001, r: 3.5, i: '3.5%', a: '46.41%' }
);

calc = function(val) {
  var success = false;
  for(i in rates) {
    if(val >= rates[i].l && val < rates[i].u) {
      $('cpm').innerHTML = '£' + Math.round(val * (rates[i].r)) / 100;
      $('mir').innerHTML = rates[i].i;
      $('apr').innerHTML = rates[i].a;
      success = true;
      break;
    }
  }
  
  if(!success) {
    $('cpm').innerHTML = ' ';
    $('mir').innerHTML = ' ';
    $('apr').innerHTML = ' ';
  }

  if(val > 20000) {
    $('cpm').innerHTML = 'call us';
    $('mir').innerHTML = 'call us';
    $('apr').innerHTML = 'call us';
  }
}

window.onload = function() {
  $('amount').onfocus = function() {
    if(this.value == 'enter amount here') this.value = '';
  }

  $('amount').onblur = function() {
    if(this.value == '') this.value = 'enter amount here';
  }
  
  $('amount').onchange = $('amount').onkeyup = function() {
    calc(this.value);
  }
}