Long runs are the bread and butter of any long-distance running goal, whether it be a full marathon or half marathon distance. They are where you build endurance and mental toughness and prepare your body for the goal distance.
But how long should your longest half marathon long run be?
The number of miles for your longest long run will vary widely based on whether you are a first-time half-marathon runner or an experienced runner and how long you train for your race.
A ballpark figure for your longest half marathon long run is between eight and 20 miles. That’s quite a range! Keep reading to see where you fit into this range and what your longest half-marathon long run should be.
The Honest Truth About Your Longest Half Marathon Long Run
The advice you’ll see most often — “peak at 12 miles, taper, race” — is roughly correct for the average half-marathon trainee but obscures what actually matters: the long run is doing four distinct physiological jobs, and the right peak distance depends on which job is your bottleneck. The runners who plateau at 12 miles typically need more time on feet for one specific reason; the runners who keep pushing past 14 miles often pay an injury cost that wouldn’t have changed their finish time anyway.
What the long run is actually adapting
The long run drives four overlapping adaptations. First, mitochondrial density and capillary growth in slow-twitch fibres — the “aerobic engine” that lets you sustain a higher fraction of VO2max for longer 1Holloszy JO, Coyle EF. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J Appl Physiol. 1984;56(4):831-8.. Second, expanded muscle and liver glycogen storage capacity — trained runners hold roughly 500–700 g of glycogen versus 350–450 g in untrained controls 2Costill DL. Muscle glycogen utilization during prolonged exhausting exercise. J Appl Physiol. 1971;31(6):834-8.. Third, increased fat oxidation at submaximal intensity — trained runners can hold marathon pace on a higher percentage of fat oxidation, sparing glycogen for the back half of races 3Holloszy JO, Coyle EF. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J Appl Physiol. 1984;56(4):831-8.. Fourth, neuromuscular and connective-tissue durability — the resistance to eccentric muscle damage and tendon stress that lets the legs hold form across a 13.1-mile race 4Arampatzis A, Karamanidis K, Albracht K. Adaptational responses of the human Achilles tendon by modulation of the applied cyclic strain magnitude. J Exp Biol. 2007;210(Pt 15):2743-53.. The first three respond to time on feet more than to specific distance; the fourth responds to gradual loading more than to peak distance.
Where the dose-response curve flattens
Long-run length correlates with marathon and half-marathon performance, but the relationship is non-linear. Tanda’s analysis of training-volume predictors found marathon performance correlates with both weekly volume and long-run length, with returns flattening past about 32–35 km of long-run distance for marathoners 5Tanda G. Prediction of marathon performance time on the basis of training indices. J Hum Sport Exerc. 2011;6(3):511-20.. For the half marathon (21.1 km / 13.1 miles), the equivalent dose-response curve flattens earlier — most data on training and half-marathon performance suggest peak long runs of 14–16 miles (22–26 km) cover the relevant adaptations, with marginal additional gain past that 6Midgley AW, McNaughton LR, Wilkinson M. Is there an optimal training intensity for enhancing the maximal oxygen uptake of distance runners? Sports Med. 2006;36(2):117-32.. The runners who push their longest to 18–20 miles for a half-marathon often see the cost on the injury side rather than the performance side — sudden volume spikes are the dominant predictor of running injury, not optimal training stimulus 7Nielsen RO, Buist I, Sorensen H, et al. Training errors and running related injuries: a systematic review. Int J Sports Phys Ther. 2012;7(1):58-75..
Long-run pace: why slow is the point
The most common long-run mistake is running it at moderate pace rather than easy. The mitochondrial and capillary adaptations the long run targets are stimulated maximally at intensities below approximately 75 percent of VO2max — the “easy aerobic” zone — and minimally at higher intensities 8Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform. 2010;5(3):276-91.. The 80/20 polarised distribution that outperforms threshold-only training is built on long, easy runs as the high-volume foundation; running long at threshold or marathon pace converts long runs into a fatigue-accumulating session that doesn’t maximally drive aerobic adaptation. The exception is the marathon-specific (M-pace) progression run done occasionally in the final few weeks before a half-marathon — the last 4–6 km at race pace, with the bulk of the run easy 9Esteve-Lanao J, Foster C, Seiler S, Lucia A. Impact of training intensity distribution on performance in endurance athletes. J Strength Cond Res. 2007;21(3):943-9..
Fueling rehearsal and the under-discussed gut adaptation
The long run is the only training session in which you can practise in-race fueling under realistic load. The gut’s capacity to absorb 60–90 g/h of carbohydrate is itself an adaptation, with 4–6 weeks of practice during long runs needed to develop tolerance 10Jeukendrup AE. Training the gut for athletes. Sports Med. 2017;47(Suppl 1):101-10.. For half marathon racing, in-race carbohydrate matters less than in marathon racing — race duration of 75–120 minutes lets glycogen alone get most runners to the finish — but practising during long runs still pays off because race-day GI distress is uncommon when fueling has been rehearsed and common when it hasn’t 11Burke LM, Hawley JA, Wong SH, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. 2011;29(Suppl 1):S17-27.. The hydration rehearsal is similar: real-world running produces 0.5–1.5 L/h of sweat depending on conditions, and the training long run is where you calibrate intake against your individual sweat rate.
When the “longest possible” long run isn’t the right goal
The candidates for shorter peak long runs are: returning runners coming back from layoff, masters runners who recover from long efforts more slowly, and runners with injury history that includes overuse or stress fractures. Hulme’s systematic review identifies training-error variables — sudden volume jumps, inadequate recovery between hard sessions — as the dominant injury predictors 12Hulme A, Nielsen RO, Timpka T, et al. Risk and protective factors for symptoms and risk of injury among long-distance runners. Sports Med. 2017;47(5):869-86.. The candidates for the longer end of the range (16+ miles) are: experienced runners with a deep aerobic base who can absorb the load, runners using the half marathon as a marathon training stepping stone, and runners targeting back-half-strong race execution who benefit from a longer time-on-feet stimulus. The honest reading: pick the long-run length that matches your bottleneck (aerobic capacity, glycogen, fat oxidation, or neuromuscular durability) and your recovery margin, and don’t chase “longer” as if it were independently virtuous.
How Long Does It Take To Train For A Half Marathon?
Assuming you have been doing some running, including being able to run (at the very least) three miles without stopping, the average time it takes to train for a half marathon is eight weeks.
Most long runs will take place on the weekends, one time per week. These weekly long run distances will gradually build up until you run at least 8 miles or as many as 20 miles at a time in training sessions.
The average time to run a half marathon race distance is about two hours, and most people can train their bodies to endure this distance by gradually increasing their weekly mileage.
Do I Have To Do A Long Run To Train For A Half Marathon?
Yes, you must do a long run to train for a half marathon, in fact weekly long runs. A long run in half marathon training prepares the body for running 13.1 miles by:
- Improving cardiovascular health13Impact of Running on Cardiovascular Health | International Journal of Sports, Yoga and Physical Activity, ISSN: 3005-5083. (2023). Internationalsportsjournal.com.
- Increasing lung capacity
- Increasing VO2 max and blood volume
- Strengthening tendons, muscles, and bones; optimizing energy pathways
- Improving neuromuscular fitness
- Building mental toughness
- Allowing the runner to optimize their fueling (gels), hydration (electrolytes), and dressing strategies
- Becoming more comfortable running at a specific run pace or race pace
Related: What to Eat Before a Long Run
If you don’t practice running for long periods of time before running your half marathon, you are setting yourself up for a world of hurt.
How Long Should Your Longest Half Marathon Long Run Be?
Your longest long run for the half marathon should be between 8 and 12 miles, depending on the length of your training plan andyour fitness level. Ideally, your long run should be at least 90 minutes.
Many runners do wonder, do I need to run 13 miles before a half-marathon? They feel that they absolutely need to reach that distance before race day to feel confident in getting to the finish line.
According to certified running coach Laura Norris of Laura Norris Running, you don’t have to run a 13 miler before your half marathon.
“Many training plans take you to 12 miles before the half marathon. Tapering and the adrenaline of race day will carry you for the final 1.1 miles,” she advises.
More advanced runners can run as long as 20 miles in their longest half-marathon long run in training. In many cases, these runners use the half-marathon race as part of their marathon training.
Running for longer than a half marathon in your training will increase mental toughness, confidence, strength, and endurance.
Here are some more specifics on how long your longest half marathon long run should be in your training cycle:
- Most 8—to 12-week half marathon training plans require runners to run a 12-mile run two weeks before their half marathon and reduce their volume before the race (aka taper).
- More advanced runners (typically those with a time goal and a specific half-marathon pace) may run up to 20 miles in their longest long run before a half-marathon.
- Some runners, likely novice runners training to finish a half marathon, may only run 8 miles ahead of their half marathon. In many cases, these runners pick a race and train on a timeline rather than letting their fitness level dictate when they run their race. It is ideal to train and then choose a half-marathon race when you are ready.
- Runners running their first half marathon with a time goal should run at least 13-14 miles ahead of their half marathon. These runners will benefit from some speed work, including fartleks, tempo runs, goal race pace sessions, and progression workouts as training runs.
- Newer runners running their first half marathon should gradually increase their long runs up to 8 miles, adding one mile per week, before picking a half marathon training plan that begins long runs at this distance.
When Should You Do Your Longest Half Marathon Long Run?
The longest long run in half marathon training is often done about two weeks before your half marathon.
Some half-marathon training plans require you to do your longest run three or just one week before your half-marathon race.
The timing depends on when your taper and a progressive reduction in training volume begins.
How Should I Pace My Long Runs During Half Marathon Training?
Your long runs should be run at an easy pace (about an effort of 6 out of 10 on the RPE scale).
An easy run effort zone is where your body learns how to use energy efficiently, build those energy powerhouses called mitochondria, and increase capillary density to supply your working muscles with more oxygen.
It also helps strengthen your musculoskeletal system safely, protecting you against injury.
In more advanced half-marathon training programs or as you near your race and do race-specific sessions, you may have some of your long runs done at tempo speeds or goal pace.
It’s important to follow a professional training plan so you can prepare as well as possible for your race, and not make anything up as you go along.
These plans will provide extra training tips, such as always performing a warm-up before your sessions and cooling down afterward and adding cross-training, strength training, and at least one rest day to your program to ensure you are reaping the maximum benefits of training.
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