Полагаю, вы можете сделать это, используя функцию шага
$('myelementid').animate({
opacity: 1,
height: 100,
percent: 100
},
{
step: function(now, fx) {
//not sure if this is 100% percent accurate
//but at least you have a value at every step of the animation
console.log( this.percent );
},
complete: function(){
//do not forget to reset percent at the end of the animaton
//so on the next animation it can be calculated from starting value of 0 again
this.percent = 0;
}
});
Надеюсь, это поможет.