I am not a veterinarian this is my opinion and experience This is what I have told clients when asked, how will I know when? I tell them to pick 3 things that their animal enjoys. When the animal no longer enjoys them then it is time. For example it may be: eating, a specific toy, going for walks, playing, taking treats etc. But you also have to be comfortable with the decision Hope this helps Lisa & her 24 paws [Posted in FML issue 4184]