Healthy nails grow about 2 cm each year. Fingernails grow four times as fast as toenails.
A nail is a horn-like keratinous envelope covering the tips of the fingers and toes in most primates. Nails evolved from claws found in other animals. Fingernails and toenails are made of a tough protective protein called alpha-keratin which is found in the hooves, hair, claws, and horns of vertebrates.
The growing part of the nail is under the skin at the nail's proximal end under the epidermis, which is the only living part of a nail.
In mammals, the growth rate of nails is related to the length of the terminal phalanges (outermost finger bones). Thus, in humans, the nail of the index finger grows faster than that of the little finger; and fingernails grow up to four times faster than toenails.
In humans, nails grow at an average rate of 3 mm (0.12 in) a month. Fingernails require three to six months to regrow completely, and toenails require twelve to eighteen months. The actual growth rate is dependent upon age, sex, season, exercise level, diet, and hereditary factors. The longest female nails are known ever to have existed measured a total of 601.9 cm, an average of 60.19 cm (23.7 inches) for each fingernail. Contrary to popular belief, nails do not continue to grow after death; the skin dehydrates and tightens, making the nails (and hair) appear to grow.