I have always gone by this guideline when it has come to putting animals down. Make a list of three to five things that the animal loves to do. As the pet can no longer do them enjoyably, cross them off, when the list is done, then it is time to consider if the quality of life is there and that it is probably time to say goodbye. Just do not be selfish. Yes, saying goodbye hurts, but when the life cannot be lived with some form of quality, is it humane to hang on? I went through this recently with one of my dogs. he was in pain, miserable and acting up. he was becoming a risk. Mercifully, we were able to find a medication that is again controlling his discomfort and helping with joint issues. I have no idea how much longer he will be with us, but he is back again to being able to live a quality of life he enjoys without pain. But if this medicine stops being effective… But what I outlined is the guide I go by. It also makes me more in tuned to my pets and what they are going through. You will know in your heart when it is time.