[jquery] Run ScrollTop with offset of element by ID

Trying to make the browser scroll to a specific ID with an added offset -

$('html, body').animate({scrollTop: $('#contact').offset().top}, 'slow');

What I need to do is to set the offset by -100px. How can I accomplish this?

var top = ($(".apps_intro_wrapper_inner").offset() || { "top": NaN }).top;   
if (!isNaN(top)) {
$("#app_scroler").click(function () {   
$('html, body').animate({
            scrollTop: top
        }, 100);
    });
}

if you want to scroll a little above or below from specific div that add value to the top like this.....like I add 800

var top = ($(".apps_intro_wrapper_inner").offset() || { "top": NaN }).top + 800;