It may take 3 to 6 months for complete re-growth to take place and toe nails might take 12 to 18 months to grow back. All these factors depend on age, season, diet and gender. They are known to grow quickly during summer than any other season because of skin dehydration. Check out http://en.wikipedia.org/wiki/Nail_(anatomy)#Growth for more information.
My fingernail bed was completely crushed and the nail fell off within three weeks. It took 4 months (sixteen weeks, give or take a day or two) to grow back completely to the end of the nail bed. I am a 49 year old Anglo male, in "very good" health. I have a "good" balanced diet.