How fast do fingernails grow?

Fingernails grow about 3.5 mm a month and toenails about 1.6 mm, based on measurements in healthy adults. Growth slows with age and in cold weather and is slightly faster in the dominant hand. A fingernail takes around 6 months to replace itself fully; a big toenail, 12 to 18 months.

Source: Yaemsiri et al. (2010), Journal of the European Academy of Dermatology and Venereology