Like Conrad, we have the vet come when we live where they will do it.
And, I have let them go in pain too long, for my own reasons. This one had pancreatitis and the vet said there was a chance she could recover with antibiotics and such. It didn't work.
when she was a healthy 12 years old or so.
This dog was not the same dog as the one above three years earlier
I still blame myself for letting her exist in pain longer than she had too.
Good luck with your decision.