I ran a few half marathons before I ran my first full, probably a good year from the first day I laced up a pair of sneakers. I would suggest that you gauge how you're doing with the half and training and see how it goes. You may be surprised at how you feel (whether good or bad) after running the half. I'd be worried about increasing your mileage too much too soon and risking injury, but that's just me. Only you know what your limits are.

Just for reference, I ran my first half with exactly 2 months prep from the first day I laced my running shoes, and ran 2 others before running a full the following Fall. I felt fine running the full, but I think having those other races under my belt really helped. Also, make sure you check the course - hills and elevation gain can really make or break a race.

Good luck!

I ran halfs for a couple years before I decided I was ready to train for a full. Personal I think one should have 6 months of 25-30 miles per week before they start an 18 week marathon training program.

I guess part of the deal is whether one is wanting to check the "I ran a marathon" box or become a runner for life.

As far as full vs. half, they are really different animals. The half is much more forgiving and you can muscle through even if you are a bit under-trained. The full is a "truth teller," you will be exposed at mile 23. There was a long thread about it last week in the fitness & exercise forum.

Also, don't forget to double your training time. Those 20 milers can take 3 or 4 hours depending on your pace.

Bottom line, play it by ear and you will know when you are ready.

I ran my first half in November 2011 last year and my first full in March 2012. If I had to do it over I would probably have given myself more time to prepare, maybe 6 months? Still, I completed it in 4:11. Best advice is not to go out too fast. Other than that get in your long runs, I think the longest I ran was 18, 20 & 22 before the full. I recently did another half and it was my best time yet. It seemed short in comparison to the full.

I would tell anyone that has run a half to definitely go for the full. It's such as sense of accomplishment and very doable. It seems hard but even a half seemed hard at first, right? So go for it.

Never forget the training plan is a simply a guideline - just numbers on a page. It doesn't know when you are feeling great or when you need some extra rest.

^^^ Excellent advice. Training plans are guidelines. Don't kill yourself trying to follow it. If you need rest, take it. If you're feeling great, run an extra mile or two.

if you're keen to do a full and you have a reasonable base, why not get a longer training programme and treat the upcoming half as part of the longer training schedule? my mate did that- he also had oodles of natural talent though and is rather genetically superior! but he had about 14 weeks between the half and the full, so got a 20 week programme and just started 6 weeks in (but kept the long run between 10-13 miles until the plan started to ask for longer distances). it worked for him but it does take an awful lot of time, dedication and motivation, possibly with a spash of determination and OCD for good measure!
the other thing you can do (if you want to) is do the half then get a full training programme and start the programme however many weeks out from the full you are- i've done that this time. i'm running a half on 20th august, and my full is on 28th oct. so my training plan for the full covers that 11 week(ish) period. but i've done a full before (and it was very hard) and have steadily increased my mileage over the past 18 months.

as for me, i started 'running' in jan last year. i eventually ran my first half in sept, then another in oct. i didn't know what to do after that and spent 4 weeks improving my 5k time. then i decided that the next logical step was to train for a full. so in dec i started a 20 week training plan which included several other halves as a part of the training. i ran my first full in may. so i think that you have the time if you want to do it. they both have their own challenges. it's more about you getting in the training without hurting yourself.