Javascript countdown timer

I'm trying to create a countdown timer in javascript for a web page.  Everything appears to be working correctly except for the seconds. I think it must be my calculation, but I don't know what else to try. Can  anyone see where I'm going wrong?

function calculate()
{
	//load dates
	var startDate = new Date()
	var endDate = new Date("May 19, 2009, 21:00:00")
	
	//load variable
	var secPerYear = 60*60*24*365;
	var secPerDay = 60*60*24;
	var secPerHour = 60*60;
	var secPerMin = 60;
	
	//seconds left right now
	var seconds = (endDate.getTime() - startDate.getTime()) / 1000
	
	//get years left value
	var years = Math.floor(seconds / secPerYear)
	
	//remove seconds from year
	seconds = seconds - (years * secPerYear)
	
	//get day value
	var days = Math.floor(seconds / secPerDay)
	
	//remove seconds from day
	seconds = seconds - (days * secPerDay)
	
	//get hours value
	var hours = Math.floor(seconds / secPerHour)
	
	//remove seconds from hours
	seconds = seconds - (hours * secPerHour)
	
	//get minutes
	var minutes = Math.floor(seconds / secPerMin)
	
	//remove seconds from minutes
	seconds = seconds - (seconds * secPerMin)
		
	seconds = (seconds / 1000);
	
		
	lblYears.innerHTML = years
	lblDays.innerHTML = days
	lblHours.innerHTML = hours
	lblMinutes.innerHTML = minutes
	lblSeconds.innerHTML = seconds

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