How Much Can a Boy Still Grow After Age 17?
Some boys are basically done growing by 17. Later-maturing boys can still gain 1 to 3 inches into their late teens. Where he sits on the puberty timeline matters more than the birthday.
The short answer
Most boys have reached about 97 to 99 percent of their adult height by age 17. That still leaves a small window. Average residual growth from 17 to full skeletal maturity is roughly 0.5 to 1.5 inches. Late-maturing boys, boys with constitutional delay, or boys whose voice change and full puberty started later can gain 1 to 3 inches after 17.
Puberty stage matters more than age
Two 17-year-olds can be in very different places. If his voice fully changed by 15 and his shoe size stopped moving a year ago, most of his growth is done. If his voice is still deepening, his shoes are still growing, or he only recently started shaving, the growth plates are still open and he has meaningful runway left.
Signs he is basically done
- Shoe size has been stable for 12+ months.
- Voice has been fully settled for at least a year.
- He was measured this year and grew less than 0.5 inch.
- Fully adult facial features and muscle mass distribution.
Signs he still has growth left
- Voice is still deepening or cracking occasionally.
- Shoe size still climbing.
- Weight gain outpacing height (pre-spurt pattern).
- Family history of late growth (dad or brothers grew after 17).
How to know for sure
A bone age x-ray of the wrist is the definitive answer. It shows how much growth plate is still open. Most pediatricians can order one. If bone age is close to 17-18, growth is nearly complete. If bone age is 15 or younger, there is meaningful growth remaining.
What actually helps late growth
Nothing dramatically. Adequate sleep, protein, and calories support whatever growth potential remains. No supplement, height-boosting spray, or online product will meaningfully change a 17-year-old's adult height. What genetics and puberty timing dictate is what you get.
Height data uses the CDC 2000 Growth Charts for boys. This page is parent education, not medical advice or diagnosis. If you have concerns about your son's growth, talk to his pediatrician, ideally with 6-12 months of measurements in hand. © 2026 The Growth Path.