As a rule of thumb, your doggies nails are too long when its paws are rested on flat ground and the nails are in contact with the ground.
When dogs walk, they make use of their front four pawpads only(tip-toe fashion), which is the correct and comfortable walking stance. As their nails get long, it reduces the angulation of tiptoe, in a way “forcing” the dog to walk on their rear paw pads which is wrong and uncomfortable. In the long term, walking in this manner may cause joint and back pain.
Have you checked your doggie’s nails today?