How Long Should Your Long Run Be? Distance, Pace and Safe Growth
Patricia Bedoya
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8
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Cover image generated with AI — © Chubby Studio S.L.
KEY TAKEAWAY
A long run is usually 1.5 to 2 times your normal run, or 20 to 30% of your weekly distance, at an easy, conversational pace. Most plans peak around 16 to 21 km for a half marathon and 29 to 35 km for a marathon. The best injury evidence says keep any run within about 10% of your longest run in the past 30 days.
A long run should usually be about one and a half to two times your normal run, or roughly a quarter of your weekly distance, done at an easy pace. If you run 30 minutes on a normal day, a long run of 45 to 60 minutes is a sensible start. How long it eventually gets depends on the race you are training for.
Those numbers are useful, but they are coaching conventions, not findings. The one rule about long-run length that has real data behind it is about how fast you grow it, and it is stricter than most plans. Here is what is known, what is habit, and what your watch can tell you along the way.
How long should a long run be for my race?
For most runners, the long run peaks a little short of the race distance for a half marathon, and well short of it for a marathon. Typical plans top out around 8 to 15 km for a 5K or 10K, 16 to 21 km for a half, and 29 to 35 km for a marathon, often with a cap of about three hours.
For a 5K or 10K
The long run here is about aerobic base more than distance. Plenty of runners training for a 10K never go beyond 12 to 15 km, and a 5K runner gains a lot from a run of 8 to 10 km. Going past the race distance is common at these lengths, and not risky if you build to it slowly.
For a half marathon
Most plans build to 16 to 19 km, and experienced runners often go to 21 km or slightly over. Running the full distance in training is optional. Arriving with several comfortable 16 km runs counts for more than one heroic 21 km run three weeks out.
For a marathon
This is where the long run is genuinely different. Plans usually peak at 29 to 35 km (18 to 22 miles), and almost none ask you to run 42.2 km before race day. The last 10 km are left to the taper, the crowd and the fitness you built over months, not to one Sunday.
The two everyday rules people use to size a long run are that it should be 1.5 to 2 times your typical run, and about 20 to 30% of your weekly distance. If you run 40 km a week, that puts the long run at 8 to 12 km. Both rules keep the long run in proportion with the rest of your week, which is their real value.
Is there any research on how long a long run should be?
Very little on the exact length. A 2020 meta-analysis of 85 marathon studies found that runners whose longest training run was longer tended to finish faster, alongside weekly distance, number of weekly runs and number of runs of 32 km or more. All of those move together, so the analysis cannot say the long run itself made the difference.
Runners who do very long long runs also tend to run more overall, have trained for more years and are often faster to begin with. A longer long run is a marker of a bigger training week, not a shortcut to one. If your week cannot support a 30 km run, adding it on its own mostly adds risk.
See what your long run really cost
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How much can I add to my long run each week?
The best evidence says keep any single run within about 10% of the longest run you have done in the past 30 days. In a 2025 study of 5,205 runners followed for 18 months, single runs beyond that point were linked to a clearly higher rate of overuse injuries, while week-to-week changes in total distance were not.
The numbers are hard to ignore. Compared with runs no more than 10% longer than the recent longest, runs 10 to 30% longer were linked to a 64% higher injury rate, runs 30 to 100% longer to a 52% higher rate, and runs more than twice as long to a 128% higher rate. It is an observational study, so it shows an association rather than proof, but it is the largest dataset on this exact question.
In practice, if your longest run this month is 14 km, your next long run is about 15 km, not 18. The long run is the session most likely to break that rule, because it is the one you deliberately make longer. We went through the full study, and why the old weekly 10% rule does not hold up, in why most running injuries are a load problem.
The 30-day window also resets when you stop. After two or three weeks off, your old Sunday distance is a large spike again, even if you ran it for years.
How fast should a long run be?
Most of a long run should be easy: a pace at which you could still speak in full sentences. For most runners that is noticeably slower than race pace, and effort or heart rate is a better guide than any pace number. The point of the long run is time on your feet, not speed.
The simplest check is the talk test, which we explain in why running feels so hard at the start: if you can talk in sentences, you are where you need to be. Going easy is what lets you run long without the run eating the rest of your week.
The exception comes late in a marathon build. Some runners put a block of goal pace into the second half of a few long runs, so they learn what race pace feels like on tired legs. That is a specific tool for experienced runners, and how it works on a flat, fast course is covered in our guide to training for the Valencia Marathon.
Why does my heart rate keep rising on a long run at the same pace?
That is cardiovascular drift. After 10 to 20 minutes of steady exercise, the amount of blood your heart pumps with each beat gradually falls, so your heart rate climbs to keep output up, even though your pace has not changed. Heat and fluid loss make it larger, which is why summer long runs feel so much harder.
If you run to a heart rate cap, your pace will slow in the second hour, and that is fine. A long run where your pace held but your heart rate drifted 15 beats cost your body more than the same run on a cool day. That gap is exactly what measuring the cardiac load of each session is meant to show.
Should I cap my long run by time instead of distance?
Many coaches do, usually at around two and a half to three hours. That cap is a coaching convention rather than a research finding, but the logic is sound: a runner at 7 minutes per kilometer spends far longer on their feet to cover 32 km than a runner at 5 minutes, and time is what the legs feel.
If you are slower, a time cap protects you from a distance target written for someone faster. A 32 km run at 7 minutes per kilometer takes about three hours and 45 minutes, which is a lot of pounding for a training day. Stopping at three hours and trusting the rest of your week is a reasonable call, not a shortcut.
Do I need to eat on a long run?
For runs of around an hour, little or nothing is needed. For longer ones, carbohydrate helps: a review in Sports Medicine recommends up to about 60 grams per hour for exercise lasting two to three hours, with less needed when the intensity is low, as it is on an easy long run.
Practising matters as much as the number. A stomach that has never met a gel at kilometer 25 will tell you so on race day. Treat a few long runs as rehearsals for race morning.
How do I know if my long runs are working?
The clearest sign is that the same long run, on a similar route and in similar weather, takes a lower average heart rate than it did a month ago, or the same heart rate at a faster pace. The second sign is recovery: how you feel, and how your resting heart rate and HRV look, the morning after.
A long run you cannot recover from in a day or two is too long for where you are right now, whatever the plan says. If your resting heart rate is still up two mornings later, or your legs stay heavy through the week, take the next long run back down a step.
FitWoody does this reading from your Apple Watch data: it scores each run against your personal cardiac load, tracks your training load week by week, and shows the next morning whether your recovery baselines are back in range. It does not decide how far you run on Sunday, but it shows you what Sunday cost.
Frequently asked questions
Should I run the full distance before a half marathon?
You do not have to. Most half marathon plans peak at 16 to 19 km, and arriving with several comfortable runs of that length is enough. Experienced runners sometimes go to 21 km or slightly beyond, which is fine as long as it stays within about 10% of their longest run in the previous month.
How often should I do a long run?
Once a week is the standard for most runners training for a race. Many plans swap it for a shorter run every third or fourth week so the body can absorb the load. Two long runs in one week is rarely worth it for recreational runners.
Is it okay to walk during a long run?
Yes. Planned walk breaks are a legitimate way to cover a long distance, and plenty of experienced runners use them in marathons and ultras. The key is to rehearse the same run and walk ratio you plan to race with, so your legs know it before race day.