function redondear(cantidad) {
var cantidad = parseFloat(cantidad);
var decimales = 3;
decimales = (!decimales ? 3 : decimales);
return Math.round(cantidad * Math.pow(10, decimales)) / Math.pow(10, decimales);
} 

	function annualCost(){
		
		var miles = document.getElementById('annualMiles').value;
		var current = document.getElementById('currentMPG').value;
		var cost = document.getElementById('avarageFuel').value;
		var annualPrice = redondear(miles / current * cost);
		var newPrice = redondear(annualPrice * (1 - (document.getElementById('avarageMPG').value/100)));
		var annualSaves = redondear(annualPrice - newPrice);
		var monthSaves = redondear(annualSaves / 12);
		var payback = redondear(7800 / monthSaves);
		
		if(!isNaN(newPrice) && !isNaN(annualPrice) && !isNaN(payback) && !isNaN(annualSaves) && !isNaN(monthSaves)){	
		document.getElementById('newAnnual').value = formatCurrency(newPrice);
		document.getElementById('annualFuel').value =  formatCurrency(annualPrice);
		document.getElementById('monthPayback').value =  formatCurrency(payback);
		document.getElementById('annualSavings').value =  formatCurrency(annualSaves);
		document.getElementById('monthlySavings').value =  formatCurrency(monthSaves);
		}else{
			alert('Please complete the fields with valid numbers');
		}
		
	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 + '.' + cents); 
	}
			
	}