Scrivo così:

codice:
var days = 0;
var difference = 0;

DataScadenza = document.Qform.DataT1.value;

today = new Date();
var day = today.getDate()
var month = today.getMonth() + 1
var year = today.getFullYear()
if (day < 10){
day = '0' + day
}
if (month < 10){
month = '0' + month
}
today = day + '/' + month + '/' + year

difference = DataScadenza - today;
days = Math.round(difference/86400000); //(1000*60*60*24));

alert(DataScadenza +'\n'+ today +'\n'+ days)
Ma days è sempre NaN....