//calculate the time before calling the function in window.onload
beforeload = (new Date()).getTime();
function pageloadingtime()
{
        //calculate the current time in afterload
        afterload = (new Date()).getTime();
        // now use the beforeload and afterload to calculate the seconds
        secondes = (afterload-beforeload)/1000;
        // If necessary update in window.status
        window.status='C' + secondes + ' s';
        // Place the seconds in the innerHTML to show the results
        document.getElementById("loadingtime").innerHTML = "<font color='red'>" + secondes + "s</font>";
}

window.onload = pageloadingtime;