When the days of quality life have ended and it becomes a struggle for your pet to just get through the day; then perhaps it is time. The decision for euthanasia can be accompanied by feelings of guilt and the tendency is to procrastinate; to postpone this very painful decision, even if you know in your heart that it is clearly the right thing to do.
But, you may take solace in knowing that you are making the best decision for you, your family and your pet at that point in time. When the time comes, we will provide as comfortable an end as possible for all concerned.