I'm so sorry
It all depends on the dog, some live days some live weeks,etc. I find the eyes are the thing to watch, you'll know when it's time
Basically it's about quality of life and keeping them as pain free as possible, there are a multitude of drugs that help keep them comfortable. Each day is precious, spend as much time together as possible and do anything special you like to do together (walks by the lake, etc)
When it comes time, have that last car ride, stop at McDonalds and get a ice cream or plain hamburger and hold him close as the vet helps him cross the bridge.
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010