Human hair grows about 0.35 millimeters per day, which works out to roughly half an inch per month and 6 inches per year. That daily figure is tiny, barely the thickness of a few sheets of paper, but it adds up steadily over time. The rate isn’t fixed, though. Your age, sex, genetics, nutrition, and even the season can shift it in either direction.
Daily, Monthly, and Yearly Averages
The standard reference range for scalp hair is 0.34 to 0.36 mm per day. Data from the Agency for Toxic Substances and Disease Registry breaks this down further by life stage: prepubescent children average about 0.41 mm per day, adolescents about 0.30 mm, adults about 0.34 mm, and older adults about 0.32 mm. Children actually have the fastest-growing hair, which surprises most people.
At the typical adult rate, you’re looking at about 1 cm (just under half an inch) per month. Over a full year, that’s approximately 6 inches, or 15 cm. If you’re growing your hair out from a short cut, expect to wait roughly two years to reach shoulder length and three to four years for mid-back length, assuming minimal breakage.
Why Growth Rate Varies by Ethnicity
Not all hair types grow at the same speed. Asian and European hair tend to grow at similar rates, while African-textured hair grows roughly 70% to 75% as fast. That difference comes down partly to the shape of the follicle and partly to how many hairs are in the resting phase at any given time. Afro-textured hair has more follicles in the resting (telogen) phase, meaning fewer strands are actively lengthening at once.
This is one reason why length retention, not just growth speed, matters so much for people with tightly coiled hair. The hair may be growing at a healthy rate but breaking before that length becomes visible. Protective styling and moisture help bridge that gap.
Sex and Age Differences
Research published in Skin Research & Technology found that healthy women generally have a slightly faster hair growth rate than men, particularly for finer strands (under 60 micrometers thick). The difference isn’t dramatic, but it’s consistent across studies. In children, boys’ hair grows about 5% to 10% faster than girls’ hair, but that pattern reverses by adulthood.
Aging has a much bigger impact than sex. Growth rates can drop by 30% to 60% in older adults, especially in areas where thinning is already visible. Even in regions less prone to hair loss, like the back of the head, the slowdown is measurable. This is why hair that once grew quickly in your twenties may feel like it’s barely moving by your sixties.
Seasonal Shifts in Growth
Hair does grow faster in summer. The average half-inch-per-month figure can climb closer to three-quarters of an inch during peak warm months, then dip to about a third of an inch in the coldest stretch of winter. Increased blood flow to the skin in warm weather and longer daylight hours both play a role. You won’t notice this day to day, but if you’ve ever felt like your hair seemed to grow faster between May and September, you weren’t imagining it.
The Growth Cycle Behind the Numbers
Each hair on your head cycles through four phases independently, which is why you don’t shed all your hair at once. The phase that determines length is the anagen (active growth) phase, which lasts 2 to 8 years for scalp hair. The longer your anagen phase, the longer your hair can potentially get before it naturally falls out and resets.
Your maximum possible hair length is essentially your growth rate multiplied by the length of your anagen phase. Someone with a 6-year anagen phase growing at the average rate would max out around 36 inches. Someone with a 2-year anagen phase, growing at the same speed, would top out around 12 inches no matter what they do. This is genetically determined and explains why some people can grow waist-length hair and others can’t get past their shoulders.
Other body hair has much shorter anagen phases. Eyebrow hairs, for example, only stay in active growth for a few months, which is why they stay short even though they grow at a similar daily rate. Facial hair grows at 0.3 to 0.5 mm per day, roughly the same range as scalp hair, but its anagen phase and density are governed heavily by hormones.
Nutrients That Affect Growth Speed
Hair follicles are among the fastest-dividing cells in your body, so they’re sensitive to nutritional shortfalls. Three nutrients have the strongest evidence linking them to hair growth:
- Iron carries oxygen to the hair follicle. Low iron is one of the most common correctable causes of slow growth and excess shedding, particularly in women.
- Vitamin D is essential for creating the cells that form new hair follicles. Deficiency is widespread, especially in northern climates.
- Vitamin C enables your body to absorb iron from food. Without adequate vitamin C, even a decent iron intake may not fully reach your follicles.
If your levels of these nutrients are already normal, supplementing more won’t push your growth rate above its genetic ceiling. The benefit comes from correcting a deficiency, not from megadosing. Biotin supplements are heavily marketed for hair growth, but deficiency is rare in people eating a varied diet, and the evidence for biotin boosting growth in non-deficient individuals is weak.
Trimming Doesn’t Change Growth Speed
Hair grows from the follicle beneath your scalp, not from the ends. Cutting your hair has zero effect on how fast the follicle produces new cells. Your genes, overall health, nutrition, and stress levels are the only things that influence the biological rate of growth.
That said, regular trims do help with length retention. Split ends travel upward along the hair shaft, causing breakage higher and higher over time. Trimming damaged ends prevents this, so your hair keeps more of the length it’s producing each month. The growth rate stays the same, but you lose less of it to breakage, which is the next best thing.
What Slows Growth Down
Beyond aging and nutrient deficiencies, a few other factors can drag your growth rate below its potential. Chronic stress pushes more follicles into the resting phase prematurely, a condition called telogen effluvium. You typically notice increased shedding two to three months after a major stressor, and recovery takes a similar timeline once the stress resolves.
Hormonal changes from pregnancy, menopause, or thyroid disorders also shift growth rates. During pregnancy, elevated hormones keep more hairs in the growth phase (which is why pregnant women often notice thicker hair), but postpartum hormone drops trigger a wave of shedding as those hairs finally enter the resting phase all at once. Thyroid imbalances, both overactive and underactive, can slow follicle activity significantly until the underlying condition is managed.
Tight hairstyles that pull on the follicle, excessive heat styling, and chemical treatments don’t change follicle speed directly, but they cause breakage that masks whatever growth is happening underneath. If your hair seems stuck at one length despite months of patience, breakage is a more likely culprit than slow growth.