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Short answer: to train for a 50 miler, plan on 20 weeks if you have already finished a 50K and run 35 to 45 miles a week. Build from about 38 to a peak of about 65 miles per week, top out with a 28-mile long run followed by a 14-mile run the next day in week 16, then taper for three weeks.
Coming from a marathon base instead of a 50K, add 4 to 8 weeks of base building first. The plan in one table:
| Phase | Weeks | Weekly miles | Long run |
|---|---|---|---|
| Base | 1 to 7 | 38 to 48 | 14 to 22 mi, start back-to-backs |
| Build | 8 to 17 | 48 to 65 | 22 to 32 mi, heavy back-to-backs |
| Peak week | 16 | About 66 | 28 mi Saturday + 14 mi Sunday |
| Taper | 18 to 20 | 65, then 45, then 30 | Shorter, race-pace touches |
A 50-miler is double a 50K and twice as hard. It's the distance where pacing, fueling, and foot care fully matter; the distance that actually deserves the word "ultra." Below: a 20-week plan from a 50K-fit base to a 50-mile finish.
Who this plan is for
- You've finished a 50K in the last 18 months
- You're running 35–45 mpw comfortably
- You have 20 weeks of consistent training
- You're prepared to spend 3+ hours running on Saturday and Sunday during peak weeks
Three phases
Weeks 1–7 (Base): 38 → 48 mpw. Long runs 14 → 22 mi. Establish back-to-back routine.
Weeks 8–17 (Build): 48 → 65 mpw. Long runs 22 → 32 mi. Heavy back-to-backs.
Weeks 18–20 (Taper): 65 → 45 → 30 mpw.
A peak week (week 16)
- Monday: rest + mobility + 20 min strength
- Tuesday: 8 mi easy with strides
- Wednesday: 9 mi with 6 × 5-min hill repeats (vert focus)
- Thursday: 7 mi easy
- Friday: rest
- Saturday: 28 mi long, on similar terrain to your race
- Sunday: 14 mi back-to-back, very slow
Total: 66 mi.
The 50-mile mistake
Most first-time 50-mile DNFs happen between mile 32 and 38. The runner went out too fast, hit the marathon mark in their planned marathon time, kept pushing, and crashed at mile 35. The fix is mental: run the first 30 miles like an easy weekend long run. Walk the climbs. Eat constantly.
A real 50-mile race starts at mile 30. The first 30 miles are about preserving the engine. The last 20 miles are where you'd been training for, all along.
Fueling: 250 cal/hr, period
A 50-mile race takes 9–14 hours for most first-time finishers. Burn rate is 350–500 cal/hr depending on size; absorption max is 250–300 cal/hr for most trained guts. The math: you'll have a calorie deficit, but if you fuel at the gut max, the deficit stays manageable.
For the full numbers by distance and body weight, see how many calories ultrarunners burn. Train this on every long run from week 9 onward. Same gels, same flask mix, same intervals. Most stomachs handle 200 cal/hr with practice; getting to 250 is a 6-week project.
Foot care
A 50-mile race destroys feet. Three rules:
- Two pairs of shoes. Most finishers swap shoes at mile 25 or 30, different last, half-size larger to accommodate swelling.
- Sock change every 4 hours. Wet socks for over an hour = blister.
- Body Glide before, during, and after. Pre-apply on toes and arches; reapply at every crew stop.
The back-to-back peak
Week 16's 28/14 back-to-back (42 weekend miles) is the workout that makes your race possible. It's also the one most likely to get skipped. Don't skip it. Plan it 6 weeks out, protect the calendar slot like a wedding.
Race-week routine
- Tuesday of race week: last hard effort, 4 × 3 min at threshold
- Wednesday: 5 mi easy
- Thursday: rest
- Friday: 2 mi shake-out + strides
- Saturday: rest, hydrate, carb-load
- Sunday: race
What's next
Finish a 50-miler and you've crossed the threshold from "ultrarunner" (theoretical) to "ultrarunner" (real). The next jump, 50 mile to 100K, is incremental: 12 more miles, similar physiology, slightly tougher pacing. The big jump is 100K to 100-mile, which is everything we wrote about in the first-100 plan.
Common questions
How long does it take to train for a 50 miler?
About 20 weeks if you have already finished a 50K and run 35 to 45 miles a week. From a marathon base, allow 24 to 28 weeks so you can build volume first.
How many miles a week should I run for a 50 mile race?
This plan peaks at about 65 miles per week, with most weeks in the build phase between 48 and 65 miles.
What is the longest run before a 50 miler?
In this plan, a 28-mile long run followed by 14 miles the next day in week 16. The back-to-back teaches you to run on tired legs without the injury risk of a single 40-mile run.
How much should I eat during a 50 mile race?
Most runners aim for roughly 200 to 300 calories per hour, practiced on every long run from about week 9. That fits the 30 to 90 g of carbohydrate per hour range in sports-nutrition guidance.
Sources: plan structure is our own, built on common ultra training practice. Fueling ranges reflect sports-nutrition guidance of roughly 30 to 90 g of carbohydrate per hour for long events (American College of Sports Medicine and International Society of Sports Nutrition position stands). Researched, not professional coaching or medical advice.
What these sessions assume you are measuring with
Every pace, zone and power figure here needs something recording it. These three cover running, long days and the bike.
Garmin Forerunner 965 AMOLED multisport with the training-load and threshold metrics most of these sessions assume you can see day to day.
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COROS APEX 2 Series GPS Watch Sapphire titanium and the longest battery in its class, which is the deciding feature once a day out runs past a few hours.
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Favero Assioma Uno Power Meter Pedal Single-sided pedal power, the cheapest honest entry into training with watts rather than estimating from heart rate.
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