Training plan for sub-3:00 marathon?

It can be done on lower mileage but I've found with athletes that 50-60 miles/week puts you in the sub-3 ballpark. 5:45 equates to 1:30/sub-3:10. You said it yourself that your threshold is in the 6:50s. You need to take your current 1hr pace & make it your 3hr pace. That's hard to do in 25 weeks because it's hard to train speed & endurance at the same time.

My advice would be to up your mileage and target a half marathon in the spring/summer. Hit a 5k and/or 10k along the way. Then run your marathon in the fall. You gotta commit to the process to run a good marathon. If you're set on doing it in 25 weeks, I'd recommend something like Pfitz, which has already been mentioned. Your workouts don't have a ton of volume. Add some volume there. Do the medium long run. Do the series of long runs with portions at marathon pace. You should make natural gains with more mileage/consistency. Is it enough to get to 2:59 in a short window? Idk. But I also think trying to force it isn't the play. You need to do workouts @ your current fitness until they show sub-3 capability rather than just running them at the pace you want to build to.

I have run 3:13 at age 47 on 25 mpw.

One can run a decent marathon on 25 mpw, let alone on 40 mpw.

@OP: M48 here, soon to be M49.

I have run sub-3:04 in 2022 on 50 kilometers (31 miles) per week for 2 months.

I share your dream of running sub-3. I will try to do it on 35 mpw for 3 months (running London). Not getting injured is my priority, so I can't jump to 50 mpw.

I think right now you're nowhere near the fitness needed to run target pace for 26.2 miles.

The good thing is you have 25 weeks.

Your odds of sub-3 imho: 25%.

Thanks for the comment. That is good to know what you did with 31 mpw. Good luck with your sub-3 attempt.

If my odds were less than 13.1%, I wouldn't have tried. But I'll take 25% or 50-50.

Lots of work ahead for me.

OP, here's another idea. As you start to do your training, start finishing your long runs with the last mile at 6:50 min/mile (4:38 min/km). As the weeks go by start increase that to two miles, three miles the next week, and so on. If you can build up to a 20-22 miler, with the 2nd half of it at sub-3-hr pace, you're getting very close.

I ran my best marathon off the 40-45 ish mpw. Most weeks I did 4 runs along the lines of:

- easy 5 mile run

- easy 10 mile run w/ last 3 miles @ MP

- hard 10 mile run, slightly slower than HMP

- 15-20 miler each week with last 6-7 miles @ MP

I would absolutely not do that at my age now. It was probably a stupid thing back then as well, but so goes life.

My ultimate suggestion would be to get something like Pfitz 55 and do as much as you can. Trim out stuff like the short 4-5 mile Saturday runs and whatever else you need to fit your schedule.

My take is that unless one is super talented there´s hardly any way to go from your shape to sub3 shape in 25 weeks AND even less at sub 40 miles per week, but what do I know

If you need a training plan or heaven forbid "advice" on this website then no, it's not going to happen.

You should be able to figure it out yourself, assuming you can run a 10k in 38 minutes.