BRF

function getDaysBetweenDates(date1, date2) {
	return Math.abs(date1 - date2) / 60 / 60 / 24 / 1000;
}

var now = new Date(),
	otherDate = new Date('2017-06-31');
  
console.log( getDaysBetweenDates(now, otherDate) );
// -> 13.517046712962962

console.log( getDaysBetweenDates(now, new Date('2018-01-31')) );
// -> 227.51642754629628

Сейчас ответы в виде 53200.1043240419230

var x = 53200.1043240419230;
console.log(x.toFixed(2))
// -> 53200.10