How long it takes to grow depends entirely on what part of your body you’re asking about. Height growth typically finishes by age 18 in males and 15 to 16 in females, but your brain keeps maturing into your mid-to-late 20s. Meanwhile, hair, nails, skin, and muscle all operate on their own timelines, some measurable in days, others in months or years.
How Long Height Growth Takes
Your height is determined by your growth plates, thin layers of cartilage near the ends of your long bones. As long as these plates remain open, your bones can lengthen. Once they fuse (harden into solid bone), you’ve reached your adult height. For most males, growth plates close by age 18, though some late bloomers continue growing slightly past that. Even the latest developers complete puberty before age 25.
The fastest height gains happen during the pubertal growth spurt. Once puberty kicks in, children grow roughly 8 centimeters (about 3 inches) per year. Boys hit their peak growth rate of about 9 centimeters per year just before sexual maturity, and their growth spurts tend to last longer than those of girls. Before puberty, children grow at a steadier pace of about 5 to 6 centimeters per year.
Hair Growth Rate
Healthy scalp hair grows about half an inch per month, which works out to roughly 6 inches per year. That’s the average, and your actual rate depends on genetics, age, nutrition, and hormonal balance. Hair on your arms, legs, and eyebrows grows more slowly and has a shorter active growth phase, which is why it never reaches the same length as the hair on your head.
If you’re growing your hair out from a short cut, expect about a year to gain 6 inches and two years or more to reach shoulder length, depending on your starting point. Keep in mind that breakage and trimming slow the process of gaining visible length even when growth itself is consistent.
Fingernails vs. Toenails
Fingernails grow at an average rate of 3.47 millimeters per month, which means a completely lost fingernail takes roughly 3 to 6 months to fully regrow. Toenails are much slower at 1.62 millimeters per month, less than half the speed of fingernails. A lost toenail can take 12 to 18 months to return completely. Your dominant hand’s nails tend to grow slightly faster, and nails grow more quickly in summer than winter.
How Long Muscle Takes to Build
Visible muscle growth follows a predictable pattern when you’re training consistently. In the first three to four weeks, you’ll notice performance gains: more reps, heavier weights, better endurance. This is mostly your nervous system learning to recruit existing muscle fibers more efficiently, not actual tissue growth.
After two to three months, slight visible changes in muscle definition start to appear, assuming you’re eating enough protein and training regularly. By four to six months, the changes become obvious to both you and the people around you. Some people notice physical improvements as early as four weeks, but substantial, head-turning changes in muscle mass generally take six months or longer.
Skin Cell Renewal
Your skin constantly replaces itself from the bottom up. New cells form in the deepest layer of the epidermis, gradually migrate to the surface, and eventually shed. In young adults, the outermost layer of skin (the part you can see and touch) replaces itself roughly every 20 days. This cycle slows with age, lengthening by more than 10 days in older adults. The total turnover time, from new cell creation to shedding, averages about 36 days in middle-aged adults.
This is why skin injuries like minor burns or abrasions take a few weeks to fully heal, and why the results of new skincare routines don’t show up overnight. You’re essentially waiting for a fresh layer of cells to cycle to the surface.
Bone Healing After a Fracture
Broken bones heal in stages, each with its own timeline. The inflammatory phase begins within hours and lasts a few days as your body sends blood and immune cells to the injury. Over the next days to weeks, a soft bridge of cartilage forms across the break. This gradually hardens into bone over several more weeks. The final remodeling phase, where the bone reshapes itself to match its original structure and strength, can take months to years.
Simple fractures in healthy adults typically feel functional within 6 to 8 weeks, but the bone continues strengthening long after the cast comes off. Larger bones, complicated breaks, and older age all extend the timeline.
Liver Regeneration
The liver is uniquely capable of regrowing itself. After surgical removal of up to two-thirds of its volume, a healthy liver can regenerate to its original size in as little as a few weeks, though several months is more common. A liver already damaged by disease or scarring takes longer. This regenerative ability is part of why living-donor liver transplants are possible: both the donor’s remaining portion and the transplanted piece grow back.
Brain Development
Your brain isn’t fully mature until your mid-to-late 20s. The last region to finish developing is the prefrontal cortex, the area behind your forehead responsible for planning, impulse control, and weighing consequences. This is why decision-making, emotional regulation, and risk assessment continue improving well past the teenage years, even though physical growth stopped years earlier.
Teeth
Permanent teeth begin replacing baby teeth around age 6 and continue erupting in stages. The last to arrive are the third molars (wisdom teeth), which typically show up between ages 17 and 21. By age 21, all 32 permanent teeth have usually erupted, though not everyone develops all four wisdom teeth, and many have them removed before they fully emerge.