Several inches. But you can make up for those lost inches if you are a late bloomer. I had the tiest diet my whole life up until i turned 18. I was 5'5, weak and skinny as all hell. I started eating alot, injecting high doses of HGH and taking Letrozole on a daily basis. Keeping your estrogen levels very low is essential in making up for lost growth. I went from 5'5 to 5'9 and im almost 21. Still growing. My growth plates have realistically frozen on x rays and my doctor still asks me if i will stop growing after he saw how i managed to grow alot after 18. This goes to show that it all depends on when you started puberty, if your bone age is younger than your actual age and etc. If you started puberty young then you should be done growing by 18 if you were exposed to normal levels of estrogen. The human body has an amazing capability to catch up on growth and delay growth plate fusion, but since estrogen fuses growth plates, it will all depend on if you manage to keep the estrogen levels in your body very low or not.