function calculate(){

  var v_importo = document.getElementById('importo').value;
  v_importo = v_importo.replace('.','');
  v_importo = v_importo.replace(',','');
  v_importo = v_importo.replace('€','');

  var v_tasso = ((document.getElementById('tasso').value.replace(',','.')) / 100) / 12;
  var sem_tasso = ((document.getElementById('tasso').value.replace(',','.')) / 100) / 2;
  var v_rate = document.getElementById('anni').value * 12;
  var sem_rate = (document.getElementById('anni').value * 2);
  var v_pot = Math.pow(1 + v_tasso, v_rate);
  var sem_pot = Math.pow(1 + sem_tasso, sem_rate);
  var v_mese = (v_importo * v_pot * v_tasso) / (v_pot - 1);
  var sem_mese = (v_importo * sem_pot * sem_tasso) / (sem_pot - 1);
  //verifica del risultato
  if ( !isNaN(v_mese) &&
  (v_mese != Number.POSITIVE_INFINITY) &&
  (v_mese != Number.NEGATIVE_INFINITY) )
  {
    Effect.SlideDown('mutuo_results');
    document.getElementById('rata').innerHTML = formatCurrency(round(v_mese));
    document.getElementById('rimborso').innerHTML = formatCurrency(round(v_mese * v_rate));
    document.getElementById('interessetotale').innerHTML= formatCurrency(round((v_mese * v_rate)- v_importo));
    
    document.getElementById('rata-sem').innerHTML = formatCurrency(round(sem_mese));
    document.getElementById('rimborso-sem').innerHTML = formatCurrency(round(sem_mese * sem_rate));
    document.getElementById('interessetotale-sem').innerHTML= formatCurrency(round((sem_mese * sem_rate)- v_importo));
  }
  //dati non validi
  else
  {
    document.getElementById('rata').innerHTML = "";
    document.getElementById('rimborso').innerHTML ="";
    document.getElementById('interessetotale').innerHTML="";
    
    document.getElementById('rata-sem').innerHTML = "";
    document.getElementById('rimborso-sem').innerHTML ="";
    document.getElementById('interessetotale-sem').innerHTML="";
  }
}
function round(x)
{
  return Math.round(x*100)/100;
}

function formatCurrency(num) {
  num = num.toString().replace(/\$|\,/g,'');
  if(isNaN(num))
  num = "0";
  sign = (num == (num = Math.abs(num)));
  num = Math.floor(num*100+0.50000000001);
  cents = num%100;
  num = Math.floor(num/100).toString();
  if(cents<10)
  cents = "0" + cents;
  for (var i = 0; i < Math.floor((num.length-(1+i))/3); i++)
  num = num.substring(0,num.length-(4*i+3))+'.'+
  num.substring(num.length-(4*i+3));
  return (((sign)?'':'-') + '€ ' + num);
}