Size Problems

I seem to be having a problem that when I make an icon in Photoshop CS or 7.0 when I save it, the JPEG options pops-up, like always, I make sure that it is under 40 KB which it always is, but lately when I upload it to Photobucket it will say the size is bigger, and it's a big difference too, once it was Photoshop said it was 18 KB and photobucket said it was 62 KB. And this is a problem, because people have been coming to me constinitely saying they can not upload my icons because they don't work, they said they were over 40 KB.

I really want to fix this problem, so any suggestions would be helpful. :)

Thanks!