As others have said, 21 miles is fine. The general rule of thumb is 20-22 miles or 3 hours should be your longest runs, whichever comes first.
Also as they said, take care of your pace… if you don’t think you’re in the shape to go significantly under 3 hours then you’re probably not recovering from your long runs.
Thanks for this guys! A minute a mile slower sounds more than I had in mind previously so glad I know that now.
I’ll aim for one last run of 22/21 miles and then taper after that. Someone said above that 5 runs a week is a lot for a taper, should I take it easier than that?
On another note - anyone got any good long running tune recommendations? Getting a bit tired of 45:33 on repeat…
I usually did a 3 week taper roughly 80% / 55% / 25% of peak weekly mileage, with workouts dropping throughout that (first week was pretty much every session but shorter, second week I dropped a couple and of sessions, in particular my second speed one, and the last week was just out a couple of times to turn over the legs.
Your marathon training plan should include for a taper appropriate to the amount of training you have been doing in the previous weeks (which is a function of what time you are aiming for).
The usual rule of thumb is to reduce mileage by about 20-30% per week, over three weeks, and reduce the intensity (so no intervals, more easy runs etc). I’d be surprised at a taper that included more than three runs in the last week though.
I’m nowhere near fit or sexy enough to be in this thread but I would like to tell you that I’ve just been for a run and feel great!
my plan had 5 runs during my taper but I had a bit of an ankle niggle so I missed quite a few.
Think the advice my physio gave me is pretty good, which is that you’re not going to do anything to substantially improve during the last 3 weeks, but you might do something that makes you slower. Take it easy, cut down the speed/number/distance of your runs, get a bit of energy back into your legs and ignore the plan if your body’s telling you it needs rest.
No need to be sexy or fit in here Bamners. Just a willingness to get out on your feet every so often is all 
Cool thanks, that’s good advice to keep in mind.
I am not at the three week mark yet so I’ll keep going as is (but not going to go over the 22 mile mark as I am worried about hurting myself) and then taper as you’ve all suggested. Thanks again!
Good luck, I did 23 miles as my longest but yeah anything over 20 should be fine. Seems like you’re smashing it, join the strava group so we can all get jealous
Everyone in this thread is fit or sexy, simply by posting in here.
must be where I’ve been going wrong!"
Thanks! We’ll see how it goes on the day… Just looked up Strava, seems good. I’ll join the group and then you can all see my horrible pacing
Urgh, is it just impossible to booze whilst training? Had 3 beers at an event last night and feel like absolute death today.
I’ve joined yer Strava group finally, thanks for the invite, will download the app once I free up some room on my phone. Good luck to anyone running this weekend!
Thank you! I made it around. Not quite the time I was hoping for, but my knee blew up again around 14miles in. A few miles of walking and a patch up job by the physios did enough to carry me through to the end.
Definitely won’t be running the Hackney Half next weekend.
Well played mate, ridiculously good effort to get round with an injury at that stage. Unbelievable.
Also, I have yet to run a half/marathon that hasn’t been run in blazing sunshine. I should start a wedding date planning service.
I’m not sure who that Anonymous donor is, but thank you!
Nice work getting through it, man! Hope the knee heals up quickly 
Great work marathon people! fair play to you Marckee for posting a time like that with an injury, must have been a long 12 miles.