The speed of nail growth depends on the person.
The answer to this question is a bit complex. The growth rate of human nails varies depending on the person, the nail in question, and the time of year. As a general rule of thumb, human fingernails grow between 0.5 inches (1 cm) and 4 inches (10 cm) per year, and several things can influence this growth rate. In fact, fingernails grow about five times faster than toenails, for the curious.
The parallel lines that run from the base to the tip of the nail become more prominent over time.
Among the many factors that influence growth rate is age. Younger people tend to grow their nails faster, especially if they follow a healthy and varied diet. To improve the strength and appearance of nails, people can consume gelatin, which will help build thicker and stronger nails. Gelatin can also contribute to hair health, although it does not significantly affect the growth rate of human hair. Imbalances in the diet can cause spots or ridges on the nails, and an overload of certain toxins can also affect the growth and appearance of the nails.
You should also consider the finger when looking at the rate of nail growth. Longer fingers seem to grow nail material faster, as do the fingers of the dominant hand. In most people, the middle finger of the dominant hand develops a nail faster, while the thumb or little finger of the other hand has the slowest nail growth rate.
Human nails seem to grow faster during the day, which means they also grow during the summer, when daylight hours get longer. As human nails grow, they can be shaped by trimming, a technique that can also be used to strengthen the edge of the nail by trimming thin, uneven material in the nail and cuticle. Some people also like to oil their nails to keep them fully hydrated, or use nail strengthening solutions if they are especially thin or bumpy.
Contrary to popular belief, human fingernails do not continue to grow after death. The illusion of growing nails is created by the dehydration that the human body experiences after death. As the body dehydrates, the soft tissues begin to shrink and separate, which can make hair and nails appear to have grown. Tissue shrinkage can also expose teeth, which explains why the dead appear to be smiling.