Why does it take one year for full growth after FUE?

The goal of a hair transplant is to provide fuller coverage while preserving a natural appearance. An assessment takes into account such factors as the apparent thickness and curl of your donor hairs, the color contrast between your scalp and hair, your hair loss pattern, your age, and many other factors. The state of the art technique is FUE (follicular unit extraction), performed with a hybrid blunt punch that minimizes graft transection to less than 4% while allowing for the use of the smallest possible punches to minimize donor site scarring while maximizing regrowth.
With FUE, the back and usually the sides of the head will be shaved down. Sometimes patients have a partial shave in which just the lower half of the back of the head is shaved, which either can be covered up by somewhat longer hair above it or if you have shorter hair it looks just like you had a “fade” hairstyle.  A no-shave FUE technique is also possible.
After a hair transplant we advise to carefully protect the transplanted hairs for the first 5 days, after which showering and increasing your activities is possible. The transplanted hair shafts will typically fall out in about 3 weeks and the new hairs will start to grow in at 3-4 months. Full growth is judged at 10-12 months. Sometimes the native hairs in the recipient area will continue to thin over time which can give the illusion of a failed transplant, when in reality most of the density is actually from the transplanted hair.
The hair follicle has to go through certain cycles, which takes a long time to go. Even naturally, hair grows slowly. It is not the fastest process, but it achieves amazing results. 

Gary Linkov, MD
Hair Specialist
Manhattan

Hair grows in different cycles. As a result, some hairs will now grow until the 6-8 month mark. By 8 months, 80% of your transplanted hairs will grow.

ON average it takes several months for the transplanted hair to start to grow after a hair transplant.  Not all the grafts grow at the same rate or all at the same time.  After around a year, you should be seeing the completion of the results from the transplant.