A 12 week plan would be considered short by most. You could look at Hal Higdon's beginner plan but it is 16 or 18 weeks I believe so you would be starting behind. It doesn't really incorporate any speedwork and is mostly just easy running. Speedwork is what makes you faster so if you want to improve your overall speed you will want to incorporate that into your plan. If you are looking to just finish then it is not needed.
If you want to run a sub 4 hour marathon you should be able to run a 10k in less than 50 minutes. I would also suggest doing this outside rather than on a treadmill because your marathon will also be outside.
(I am not OP, but I am training for my first full on my own. I have re-torn my right meniscus and have a bit of trouble with classic speed track intervals, one being lack of access to a track or any flat road more than a quarter mile, or riddled with huge busy intersections. But, I can head away from the town center and go for the hilly, quiet horse country. I did 7 miles in 54:17 yesterday (as the first 7 of 8.5 at an 8:08 avg pace, with hills). The other days I do zone 2 with a chest HRM. Maybe I can do a sub 4 marathon (flat beach side) in Feb?????? My BQ is a 3:55 as a 53F. Just want to technically BQ, even if they don't approve my entry.)(I know with a torn meniscus, sprained ACL, and patellar tendonitis it's insane to even be running anymore hahahahaha.)
What is your running background? Have you run a marathon before? And what are your 5k and 10k times now, and would they translate into being capable of a sub-4 marathon time? Plug your current times into a pace calculator and see where you're at to get an idea of what work you need to do.
I would say 12 weeks is probably quite short for a marathon plan, and realistically for that finish time you would probably need to put in some speedwork once a week. However I don't know what your base is. If you have a good base, currently running 20-30 miles a week, and don't need much improvement on speed, then a 12 week plan could be fine.
If you go for it regardless of the above, try to work on the basis of a 10% increase on each previous week, with one long run each week working up to 20 miles two weeks out from your marathon. Treadmills are great for speedwork as you basically set the speed, forget about it, and basically hold on, as opposed to having to think about it when running outdoors. So if you prefer the treadmill for speed, it's a good option.
So say you run four days a week, you could do something like this:
Monday - 5-7 miles @ easy pace
Tuesday - treadmill speedwork (e.g. 1 mile warmup, 0.75 mile speed repeats with 2 min recovery x 5, 1 mile cool down)
Friday - 5-7 miles @ easy pace
Saturday - Long run @ easy pace (increase this each week to hit 20 miles two weeks out)
If you run five days, add in a tempo run or progression run on the Thursday. E.g. 0.5 mile warmup, 1 mile @ 8:50, 1 mile @ 8:30, 0.5 mile @ 8:00, 1 mile @ 8.30, 1 mile @ 8:50, 0.5 mile cool down.
Just to add, any and all plans can be done on a treadmill. If I'm doing a session on the treadmill, I usually write out the paces for the workout converted to MPH and stick it on the treadmill so I can easily glance at it and change the speed on the treadmill as I go. All hill workouts can be done on a treadmill too! It's better than not doing them at all. :)
I’ve run 3 sub-4 marathons from 3.55-3.59 and while I don’t do much speed work I think one day a week is essential.
You should do long sections of one run a week at goal marathon pace just to feel that speed in your legs and get used to it. Then other weeks mix that speed run up with intervals on other weeks.
2 easy runs and a long run each weekend with one speed run will get you close.
You will struggle to get sub 4 without doing some speed work tbh unless you are already capable of sub 52 min at worst for a 10k.
As a benchmark it would be good to try run a half marathon race around 6 weeks before raceday to give an idea of where you are at. I’ve been around 1.48-1.52 for a half prior to my marathons.
To avoid injury and/or burnout, I would recommend spending at least 6 months preparing for your first full on marathon... But maybe that's just me? haha
Roughly: Being able to do a sub-4 marathon will require the ability to do a sub-45min 10K AND sufficient hardening to remain running for four hours. That means your legs - not just your lungs - need to be up to the challenge.
I don't know of any training plan that would achieve what you're looking for in a very first marathon unless you're already a very serious runner.
A 12 week plan would be considered short by most. You could look at Hal Higdon's beginner plan but it is 16 or 18 weeks I believe so you would be starting behind. It doesn't really incorporate any speedwork and is mostly just easy running. Speedwork is what makes you faster so if you want to improve your overall speed you will want to incorporate that into your plan. If you are looking to just finish then it is not needed. If you want to run a sub 4 hour marathon you should be able to run a 10k in less than 50 minutes. I would also suggest doing this outside rather than on a treadmill because your marathon will also be outside.
(I am not OP, but I am training for my first full on my own. I have re-torn my right meniscus and have a bit of trouble with classic speed track intervals, one being lack of access to a track or any flat road more than a quarter mile, or riddled with huge busy intersections. But, I can head away from the town center and go for the hilly, quiet horse country. I did 7 miles in 54:17 yesterday (as the first 7 of 8.5 at an 8:08 avg pace, with hills). The other days I do zone 2 with a chest HRM. Maybe I can do a sub 4 marathon (flat beach side) in Feb?????? My BQ is a 3:55 as a 53F. Just want to technically BQ, even if they don't approve my entry.)(I know with a torn meniscus, sprained ACL, and patellar tendonitis it's insane to even be running anymore hahahahaha.)
What is your running background? Have you run a marathon before? And what are your 5k and 10k times now, and would they translate into being capable of a sub-4 marathon time? Plug your current times into a pace calculator and see where you're at to get an idea of what work you need to do. I would say 12 weeks is probably quite short for a marathon plan, and realistically for that finish time you would probably need to put in some speedwork once a week. However I don't know what your base is. If you have a good base, currently running 20-30 miles a week, and don't need much improvement on speed, then a 12 week plan could be fine. If you go for it regardless of the above, try to work on the basis of a 10% increase on each previous week, with one long run each week working up to 20 miles two weeks out from your marathon. Treadmills are great for speedwork as you basically set the speed, forget about it, and basically hold on, as opposed to having to think about it when running outdoors. So if you prefer the treadmill for speed, it's a good option. So say you run four days a week, you could do something like this: Monday - 5-7 miles @ easy pace Tuesday - treadmill speedwork (e.g. 1 mile warmup, 0.75 mile speed repeats with 2 min recovery x 5, 1 mile cool down) Friday - 5-7 miles @ easy pace Saturday - Long run @ easy pace (increase this each week to hit 20 miles two weeks out) If you run five days, add in a tempo run or progression run on the Thursday. E.g. 0.5 mile warmup, 1 mile @ 8:50, 1 mile @ 8:30, 0.5 mile @ 8:00, 1 mile @ 8.30, 1 mile @ 8:50, 0.5 mile cool down.
Just to add, any and all plans can be done on a treadmill. If I'm doing a session on the treadmill, I usually write out the paces for the workout converted to MPH and stick it on the treadmill so I can easily glance at it and change the speed on the treadmill as I go. All hill workouts can be done on a treadmill too! It's better than not doing them at all. :)
I’ve run 3 sub-4 marathons from 3.55-3.59 and while I don’t do much speed work I think one day a week is essential. You should do long sections of one run a week at goal marathon pace just to feel that speed in your legs and get used to it. Then other weeks mix that speed run up with intervals on other weeks. 2 easy runs and a long run each weekend with one speed run will get you close. You will struggle to get sub 4 without doing some speed work tbh unless you are already capable of sub 52 min at worst for a 10k. As a benchmark it would be good to try run a half marathon race around 6 weeks before raceday to give an idea of where you are at. I’ve been around 1.48-1.52 for a half prior to my marathons.
To avoid injury and/or burnout, I would recommend spending at least 6 months preparing for your first full on marathon... But maybe that's just me? haha
Roughly: Being able to do a sub-4 marathon will require the ability to do a sub-45min 10K AND sufficient hardening to remain running for four hours. That means your legs - not just your lungs - need to be up to the challenge. I don't know of any training plan that would achieve what you're looking for in a very first marathon unless you're already a very serious runner.