Quick summary
- The rule: run most long runs 45–90 seconds per km (about 1:15–2:25 per mile) slower than your goal marathon pace.
- Sub-4 example: marathon pace is 5:41 per km, so long runs sit at about 6:26–7:11 per km.
- Feel: you should be able to talk in full sentences for most of the run.
- Exception: in the final 8–10 weeks, finish some long runs with 5–16 km at marathon pace.
- Hot day? Run by effort or heart rate and let the pace slow.
The long run is the most important session in marathon training, and the one runners most often run too fast. A long run that leaves you wrecked for three days costs you more training than it gives back. The right pace feels almost too easy for the first half, and still lets you finish strong.
Why slower long runs make you faster
The long run builds the things that matter most after 30 km of a marathon:
- More capillaries and mitochondria in your leg muscles, so they use oxygen better.
- Better fat burning, which saves limited carbohydrate stores for later in the race.
- Stronger tendons, bones and connective tissue that can handle hours of impact.
- Practice: time on your feet, fueling on the move, and testing your race kit.
All of these come from time spent running, not from running fast. Push the pace and you add fatigue and injury risk without adding much benefit, and you'll be too tired to run your midweek sessions properly.
Long-run pace by marathon goal
Find your goal finish time. Easy long-run pace is about 45–90 seconds per km slower than marathon pace. Use the slower end early in a training block, on hot days and on hilly routes.
| Marathon goal | Marathon pace per km (per mile) | Long-run pace per km (per mile) |
|---|---|---|
| 3:00:00 | 4:16 (6:52) | 5:01–5:46 (8:04–9:17) |
| 3:30:00 | 4:59 (8:01) | 5:44–6:29 (9:13–10:25) |
| 4:00:00 | 5:41 (9:09) | 6:26–7:11 (10:22–11:34) |
| 4:30:00 | 6:24 (10:18) | 7:09–7:54 (11:30–12:43) |
| 5:00:00 | 7:07 (11:27) | 7:52–8:37 (12:39–13:51) |
| 5:30:00 | 7:49 (12:35) | 8:34–9:19 (13:48–15:00) |
For other goal times, take your marathon pace from our marathon pace chart and add 45–90 seconds per km.
Pace, effort or heart rate?
Pace is a useful guide, but effort is what your body responds to. On hot, humid or hilly days the same pace costs far more effort, so use one of these instead:
- The talk test: you can speak in full sentences. If you can only manage a few words, slow down.
- Heart rate: roughly 65–78% of your maximum heart rate for most of the run is a common easy-run guide. A chest strap is more accurate than a wrist sensor.
- Perceived effort: about 3–4 out of 10 for the first two-thirds.
If your pace drifts slower in the final third at the same effort, that's normal, especially in heat. Don't chase the number.
How long should the long run be?
For most marathoners, the long run builds gradually to a peak of 28–32 km, or about 3 hours, whichever comes first. Running for more than about 3 hours adds a lot of fatigue for relatively little extra benefit, which is why slower runners often cap long runs by time rather than distance.
A typical progression adds 1–3 km per week, with a shorter recovery long run every third or fourth week.
When to run marathon pace on long runs
Once you have a solid base, usually 8–10 weeks before the race, some long runs should include marathon pace. This teaches your legs and your fueling to work at goal pace while tired.
| Weeks before race | Long-run format (example for a sub-4 runner) |
|---|---|
| 10–12 | 24 km easy, last 5 km at marathon pace |
| 7–9 | 26–27 km easy, last 8 km at marathon pace |
| 5–6 | 29 km easy, last 10–13 km at marathon pace |
| 3 | 22 km easy with 2 × 5 km at marathon pace |
Keep these to every other week at most, with fully easy long runs in between. Our sub-4 hour marathon training plan schedules them for you.
Five long-run mistakes
- Racing your training partners. Run your pace, not the group's.
- Starting fast. The first 5 km should feel almost too slow.
- Not fueling. Practise race-day fueling on every run over about 90 minutes. Start taking carbohydrate 30–40 minutes in.
- Ignoring the weather. In heat, slow down 10–30 seconds per km or more and drink to thirst.
- Skipping recovery. Easy running or rest the day after a long run lets the adaptations happen.
FAQ
How much slower than marathon pace should long runs be?
Most long runs should be 45–90 seconds per km (about 1:15–2:25 per mile) slower than goal marathon pace. Run toward the slower end early in training, in heat and on hills.
Is it bad to run long runs too fast?
Yes, if it happens often. Fast long runs add fatigue and injury risk, and make it harder to recover for your midweek workouts. The benefits of a long run come mainly from time on your feet at an easy effort.
Should I run 32 km (20 miles) before a marathon?
Not necessarily. Many runners peak at 28–32 km. If 32 km would take you more than about 3 hours, capping the long run at 3 hours is usually a better trade-off.
Should long runs be at marathon pace?
Most should not. In the final 8–10 weeks, include marathon-pace sections in some long runs, typically the last 5–16 km, but keep the rest easy.
What heart rate should a long run be?
A common guide is about 65–78% of maximum heart rate for most of the run, allowing a gradual rise toward the end. Heart rate rises in heat, so expect a slower pace at the same heart rate on hot days.
This article is general training information, not medical advice. Check with a doctor before starting a new training programme.