A ver si te sirve este codigo:
Código:
<html>
<div align="center">
<script languaje="JavaScript">
function getTime() {
now = new Date();
y2k = new Date("Dec 31 2014 23:59:59");
days = (y2k - now) / 1000 / 60 / 60 / 24;
daysRound = Math.floor(days);
hours = (y2k - now) / 1000 / 60 / 60 - (24 * daysRound);
hoursRound = Math.floor(hours);
minutes = (y2k - now) / 1000 /60 - (24 * 60 * daysRound) - (60 * hoursRound);
minutesRound = Math.floor(minutes);
seconds = (y2k - now) / 1000 - (24 * 60 * 60 * daysRound) - (60 * 60 * hoursRound) - (60 * minutesRound);
secondsRound = Math.round(seconds);
sec = (secondsRound == 1) ? " segundo" : " segundos";
min = (minutesRound == 1) ? " minuto" : " minutos, ";
hr = (hoursRound == 1) ? " hora" : " horas, ";
dy = (daysRound == 1) ? " día" : " días, "
document.getElementById("counter").innerHTML = "Faltan " + daysRound + dy + hoursRound + hr + minutesRound + min + secondsRound + sec + " <br />para el 2015!!!";
newtime = window.setTimeout("getTime();", 1000);
}
</script>
<body onLoad="getTime()">
</div>
<p style="color:#000000;text-align:center;" id="counter"></p>
</body>
</html>
Está sacado de: http://www.mundonets.com/tecnologia/hacer-contador-cuenta-regresiva-en-javascript/