Very hard question to answer. Like Jessica, my first dog did not have any good days left. She had some sort of seizure which left her with an involuntary head bob and an inability to walk. I carried her outside five times a day with the belief that she was going to get better, and she was in and out of the hospital for a month. I finally realized one night when I was sitting on the floor spoon-feeding her Gerber baby food and she peed all over herself (sorry for the graphic), that I could not do this to her anymore. So my answer would be a bad day, because if I thought she was still having any good days I am not sure I could do it. I don't know for sure what I will do in the future, it is a very hard decision to make in any case. I hope you have a long time before you have to make this decision. Give Nanook a great big bear hug for me.