It really depends on you! It took me about 20 lbs to notice a difference, I was over 200 pounds to start though. The smaller you get the more quickly you notice changes. One way to never notice though is to keep giving up! Keep at it!!!
Take weekly measurements, start at your neck and measure EVERYTHING (neck, chest, bust, under bust, upper arm, waist, belly at bellybutton, hips, thigh, calf). The tape measure will show losses before your eyes will or even before it's terribly noticeable in your clothes. Plus there are weeks when the scale can stall but your measurements can keep going down.