This is a hard question, which I'm not sure of the answer. I'm guessing I'll be facing it with Bear in the next few years. I'd like to say I'd do it on a good day but I'm not sure I can. I think I'd always wonder if he still had some good days left. I've never had to decide when it's time, Sandy my RB terrier took the decision out of my hands. He collapsed one night on our deck. After a trip to the emergency vet and then our own vet he passed away the next night from heart failure. The vet had recommended giving him 24 hours to see if he responded to treatment, but I knew the next day I'd have to make that decision. I like to think he knew how hard it would be for me to do it and he decided to save me that pain.