How much time gap is ideal between 2 FUT hair transplants?

It is best to see your doctor for a recommendation based on your results.  Most doctors may say one year is a good interval but there may be instances where you can shorten the interval.

If your surgeon feels your donor site has recovered and you know you are going to want more grafts, a second procedure at eight months is fine.

Generally it's best to wait until the final results of the first transplant have appeared, so the second can be made to supplement it correctly. 8-10 months is the bare minimum but I'd recommend a year just to really get an idea of what the state of your hair is post-transplant.

If you are happy with your 1st FUT, the ideal place for you to go to get this answer is your original surgeon.  He/she can look at your donor area and the progress of your grafts and make the appropriate recommendation. I have done the 2nd FUT as soon as 8 months from the original one. 

Thank you for your question. You didn’t submit a photo or details about your history, asking about the ideal time between two FUT transplants. You state you had a hair transplant about 8 months prior, and your doctor said you have a loose scalp so you could have another FUT transplant, so you want to know the ideal timeframe and the optimal method. 
Without any further details, I can share with you a little about the philosophy of hair transplant, and what we’ve done in our practice which has been a significant benefit for those patients who already had a hair transplant. A little background: I’m a Board-certified cosmetic surgeon and Fellowship-trained oculofacial plastic and reconstructive surgeon. I have been in practice in Manhattan and Long Island for over 20 years.  I’m also the founder of TrichoStem™ Hair Regeneration Centers, a system I developed over the course of several years, now going on over 7 years, which is a non-surgical alternative to hair transplant, but also an option to help people who’ve already had transplant. This uses a regenerative medicine technology which interestingly evolved from us doing hair transplants.
The indication for hair transplant is the absence of hair in a given area where you want hair. You get that hair from the donor area, which is limited to a narrow band behind the scalp. FUT, or strip surgery, is optimal for number of grafts yielded, and quality of grafts. This is easily debated now that FUE or follicular unit extractions have become so popular. In terms of the quality of hair and the yield, you are best served with FUT, but there are pros and cons.
That said, once the transplant is done, if you ask the patient or a physician like myself about the best timespan between transplants, I would say as long as possible. The transplant surgeon may have a vision on what can provide the optimal cosmetic result, but the harsh reality is tapping the limited donor area for a second transplant where there’s less and less transplantable hair. Hair transplant is a race between your rate of hair loss and the ability of a hair transplant to compensate for some of that loss. You can never fill or restore the volume of hair that is lost, but you can try to create a perception of developing a frontal hairline to improve the density in the front to mid-scalp area.
In our practice, we have developed a treatment called Hair Regeneration. This treatment evolved 7 years earlier when we were doing hair transplants in significant numbers, and wanted to: maximize the yield of the transplants, the grafts to heal better, and the donor area to heal better. What ultimately happened is we also found thinning hairs became thicker. Over the course of several years, I developed an algorithm and system for both men and women with thinning hair. We don’t have to transplant hair for people who have hair, rather we’re able to reactivate hair that’s not growing, thicken existing thinning hair, and stop progression. We are able to accomplish that without depending on other modalities for about 5 years duration for the overwhelming majority of patients. There are always exceptions, but essentially, 99% of men and women, we’ve been able to show benefit.
What’s interesting is many people have come to our practice for this treatment from around the world for thinning hair, but we also have patients from around the world who have had a transplant. When they had the transplant done and noticed they were still losing hair, they tried to look for an alternative to a second transplant, and that’s when they learn about Hair Regeneration. They actually come in for treatment because it’s not like we’re saying never get another transplant, but if you can stretch out the time as long as possible physiologically, then you are not going to run out of hair before you run out of transplantable grafts. For example, if a person starts losing their hair in their 20s, we’ve had patients who had 4 or more transplants by their mid to late 30s because they’ve lost their native existing hair - they ended up looking like they didn’t have much hair. It’s a frustrating situation because they’ve lost their native hair, and the transplanted hair could not come close to providing the volume and density they desired.
From a surgical perspective, the time between the FUT transplants, usually allow a year for wound healing, remodeling, and settling before you would do another transplant. That’s more advantageous for the surgeon and you for the healing process and graft yield. If you’re thinking long-term, you have to think what can you do for stabilization, and slow down progression. This is where Hair Regeneration has been a tremendous value to people who had hair transplant and want to minimize the number of transplants they do because the donor area is limited. Yes, people can get body hair transplantation, and I have seen very good results with that. I think when it comes to the simplicity of our procedure of getting injections, to restore the hair growth and help the quality of the hair grafts, then the injection can be a very viable alternative to doing a second transplant. To answer your question, I generally told my patients when we were doing a lot more transplants that waiting for a year and beyond is advisable. I would also explain to them we’re still trying to achieve a certain aesthetic result, but you may lose more hair and have a limited amount of donor hair once a second transplant is done.
In our current practice, the answer to your question would be to wait as long as possible, and learn about the regenerative technologies such as Hair Regeneration that can help you avoid, or prolong the time before another transplant. With our results of 5 years, that’s a significant amount of time when someone has already lost enough hair that they need a transplant. At a certain point, the threshold of hair coverage becomes so low that a little loss results in a lot more scalp exposure. If you can save and thicken those hairs, I would argue that it exceeds the results of not just one, but two transplants. I hope that was helpful, I wish you the best of luck, and thank you for your question.

Time between hair transplants should be at least 8 months as you will get 80% of the results by the 8th month and your doctor will know where to put it\\the next round of grafts