I cut the front paws about twice a month, and the back paws about once a month.

Harry gets a trim more often than the others because he's my couch shredder. His also get cut so short that there might as well not be a nail there (BAD Harry! ) The more often you cut their nail, the shorter the vein that is inside their nails becomes. The shorter the vein, the shorter you can cut the nail. Harry has minimal vein in his front paws from me trimming so often. If you've never trimmed their back paws before, just be careful not to clip the vein - owie.