Hi there,This Chart
will help you tell if your cat is just a little plump or really overweight.
What food have you been using to try and slim your cat down, or have you been approaching this by trying to increase exercise only?
Do you leave dry food out at all times, or offer food at certain times of the day - if so, how much?
If your kitty an indoor only cat? What kinds of toys are it's favorite (not all cats respond to catnip - does yours?) Does your cat like to climb, to bat balls, or prefer long toys it can wrestle with and rabbit-kick?
A little more information would be helpful.