A Guide To Trimming Your Dogs Nails
How often do their nails need to be trimmed? That will depend on the dog and it's lifestyle, however most dogs will need their nails trimmed every four to six weeks.
What happens if I don't cut my dogs nails? It may present a potential health problem because the nails are very strong and tend to grow in a downward curve, an unattended nail may grow too long and cause the entire tendon and bone structure of the foot to weaken. Over time, long nails continually striking onto the ground when it walks will only put excessive pressure on the bones and tendons and cause discomfort. Similarly, unattended dew claws will curve back into the pad and can cause a puncture wound that is painful for the dog and can become infected.
So basically you want to cut off enough to create a healthy short nail.
Here is a diagram which explains a bit about your dogs nails and shows a guideline of where you should trim them.