How long should your longest run be before a marathon?
For some runners the answer is 32 km. For others it is less, or it is better judged by time instead of distance. Here is the practical way to set your longest run without wrecking the next week of training.
· 6 min read · Training
The usual answer is 20 miles or 32 km. That answer is useful, but only up to a point.
Your longest run before a marathon should be long enough to build endurance and confidence, but not so long that it wrecks the following week of training. For some runners that means 32 km. For plenty of others it means using time on feet instead.
The quick answer
Two rules make this much simpler:
- Your longest run should usually be around 25% to 30% of your weekly mileage. - For most recreational runners, the cost starts to outweigh the benefit once the run pushes much past 3.5 to 4 hours.
That is why the same 32 km run can be perfect for one runner and too much for another.
| Goal marathon time | Typical longest run | Time on feet | |---|---|---| | Sub 2:30 | 35-40 km | 2:15-2:45 | | Sub 3:00 | 32-38 km | 2:40-3:10 | | Sub 3:30 | 28-34 km | 3:00-3:30 | | Sub 4:00 | 26-32 km | 3:10-3:45 | | Sub 5:00 | 24-30 km | 3:30-4:00 | | 5:00+ | 22-26 km | cap around 4:00 |
If your target pace means 32 km will take well over 4 hours, it is usually smarter to cap the run on time rather than forcing the distance.
If you want the whole progression worked out for you, the [marathon training plan](/run-planner) can build long runs around your current mileage, goal time, and race date.
Why the 32 km rule works for some runners
Long runs matter because they build aerobic durability, improve fuel use, and prepare your legs for sustained impact. But marathon training is not about one heroic session. It is about stacking enough good weeks together to arrive healthy.
That is why 32 km became such a common benchmark. It is long enough to create a serious endurance stimulus, but short enough that many runners can recover from it and keep training normally.
The problem is that 32 km is a distance rule, not a recovery rule. A runner covering it in 2:30 and a runner covering it in 3:50 are not doing the same session.
Use weekly mileage and time, not ego
The cleanest way to decide on your longest run is to use both volume and time.
If you run 60 km per week, a long run around 18 to 20 km is proportionate. If you run 80 km per week, something in the mid-20s makes more sense. That is the logic behind the 25% to 30% rule used in many established marathon systems.
Then apply the time cap. Once a long run starts pushing past about 3.5 to 4 hours, recovery gets more expensive. For slower runners, that usually matters more than the exact distance on the watch.
This is also why first-time marathoners often get into trouble chasing someone else’s 20-mile long run. It looks normal on paper, but it may be too large a percentage of their week.
How many peak long runs you actually need
Most marathon plans work better with 2 to 3 long runs near peak distance, not one giant effort.
A simple example looks like this:
- Week 1: 28 km - Week 2: 30 km - Week 3: 32 km or your time-capped equivalent - Week 4: step back to 22 to 24 km - Then start tapering 2 to 3 weeks before race day
That step-back week matters. It is where the training starts to consolidate instead of just piling on fatigue.
How to pace the long run
Most runners make their long run too hard.
For the bulk of marathon training, your long run should feel easy enough to hold a conversation. For many runners that lands roughly 45 to 90 seconds per kilometre slower than marathon pace, but effort matters more than the exact number.
If you are training for your first marathon, keep the longest runs simple. Easy pace is enough. More advanced runners can sometimes finish the final section at marathon pace, but that only works if recovery stays under control.
If pacing is still fuzzy, [long run pacing strategy](/blog/pacing-strategy-race) is the better place to dial in effort.
Fuel your long runs like practice for race day
Any run over about 90 minutes is a good chance to rehearse fuelling.
- Aim for roughly 30 to 60 g of carbohydrate per hour. - Drink consistently instead of waiting until you are badly thirsty. - Practice with the same gels or drinks you expect to use in the race.
The longest run is not just about fitness. It is also where you find out whether your fuelling plan actually works. The [marathon fuelling calculator](/tools/marathon-fueling-calculator) makes that easier to test before race day.
Do you need to run the full marathon in training?
No. For most runners that creates too much fatigue for too little extra benefit.
What matters is building enough long-run volume that race day feels like an extension of training, not a complete jump into the unknown. The taper, crowd support, and race-day focus do the rest better than a 42.2 km training run ever will.
FAQ
**Do I need to run 32 km before my marathon?** No. It is a useful benchmark, not a law. If 32 km would put you well beyond 4 hours, cap the run on time instead.
**What if my longest run felt awful?** One bad long run is normal. Review pacing, fuelling, weather, and accumulated fatigue, then move on to the next week instead of trying to force a redo.
**Can I use back-to-back long runs instead?** Sometimes. Two medium-long runs on consecutive days can work well for experienced runners who do not recover well from one very long outing.
**How far out should the longest run be?** Usually 3 weeks before race day, sometimes 4 if you know you carry fatigue for longer.