How long does FUE Hair Transplant last?

Thanks for the question. Results of Hair Transplant surgery is permanent because the hair taken from the back of the scalp are genetically prone to DHT Hormones. In male pattern hair loss, the back of the scalp mostly never loses hair. On the other hand, the hair transplant surgery will not avoid the shedding of the non-transplanted hair. I wish you all the best.

FUE hair transplant normally is a permanent solution for hair loss except some cases. But after the 1 st one if the density of recipient area doesn't satisfies your you can have one more to increase the density. 

Transplanted hairs should last forever. If you are asking about the how many grafts survive the surgery to grow new hairs, it can vary from patient to patient and doctor to doctor.  Some PATIENTS may be poor FUE candidates and great number of harvested grafts may not survive.  This is independent of doctor's skill or the type of instrument used, such as ARTAS or Neograft.   Some DOCTORS may be poor FUE surgeons and great number of harvested grafts may not survive despite the use of latest technology such as ARTAS or Neograft.  In some cases all the FUE grafts may survive and produce great hairs, but if the doctor was not skilled in his technique (despite the use of ARTAS or Neograft)  the overall results (with all the hairs that grew) may look horrible and unnatural!  A bad hair transplant is like herpes.  It's for life.

In theory, hair transplant is meant to be a permanent solutions to the problem of baldness and thinning hair. Even in some specific cases, if it doesn't last a lifetime, it is extremely long lasting and one of the most successful treatments to regain lost hair.
The transplanted hair follows the behaviour of the donor area and will continue to grow as it did in the donor area.
No two cases are the same, so comparing yourself to another before / after picture on the internet and imagining an expected result based on a Google search is not the right approach. Ideally, you should look for a well experienced and qualified surgeon in your city and visit him / her for a consultation.
This is because, permanence of hair transplant is something that depends a lot on suitable candidacy and your surgeon setting the right expectations. Your cosmetic surgeon should be able to evaluate your suitability based on your age, genetics, health record and family history. It is then that the surgeon and patient mutually set the right expectations.

FUE Transplant Results are permanent and as long as the grafts are carefully selected from the permanent zone they won't be affected by male patterned baldness process.  Occasionally patients may see thinning even on their donor area with advanced age.  In those cases transplanted hair may follow the same thinning, but it won't happen in every one.

The answer is in another question, how long will you live? If the hair came out of the donor scalp area it should last your lifetime growing about 1/2 inch per month.