Your long run should be roughly 20 to 30% of your current weekly mileage, held to that share as you build, and capped near 22 miles or 3 hours, whichever hits first. That is the answer for most runners, 5K to marathon. Everything below is the calibration: how the ratio changes with race distance, how to build the mileage safely, and the pattern I watch for when a long run stops paying back.
There is no single number, and the reason is simple. A 20-mile long run at 60 miles a week is a workout. A 20-mile long run at 30 miles a week is a race. Same distance, different training stress. The number that matters is the ratio, not the miles.
The long run as a share of your weekly volume
Across the athletes I coach, the healthy range for the weekly long run sits between 20 and 30% of total weekly mileage. Under 20% and it is not stimulating enough to develop the aerobic system it exists to develop. Over 30% and it starts eating the rest of the week, in the form of a stale Tuesday workout and a Thursday that feels like Friday.
The math, made concrete:
| Weekly mileage | Long run range | Where it should live |
|---|---|---|
| 20 mpw | 4–6 mi | The upper end. Base is thin, the long run is the aerobic engine. |
| 30 mpw | 6–9 mi | 25% is the honest middle. Do not chase 10 yet. |
| 40 mpw | 8–12 mi | Now you have room. 12 is a healthy ceiling here. |
| 50 mpw | 12–15 mi | Marathon-ready territory begins. |
| 60 mpw | 14–18 mi | The long run is a workout, not the whole week. |
| 70+ mpw | 16–22 mi | Elite-adjacent ratios. Cap earlier, not later. |
Two things fall out of this table that most training PDFs get wrong. A runner on 25 miles a week should not be doing 18-mile long runs, even if the plan calls for it. The ratio is 72%, and the following week will be a wreck. And a runner on 60 miles a week does not need 24 to prepare for a marathon. 20 is plenty. There is no bonus for going further than the body can absorb.
How it changes with the race you are training for
The 20 to 30% share is the ceiling for most weeks. The exact number inside it moves with the distance you are training for, because the long run is doing different work in each block.
- 5K and 10K training. The long run is aerobic support, not the star. Keep it near 20 to 25% of weekly volume. A 30-mile-a-week 5K runner does not need 12-mile long runs. 7 to 9 is doing the job. The tempo session is the workout that decides your 5K, not the Sunday long run.
- Half marathon training. The share stays similar, but the ceiling moves up. Peak long runs of 12 to 15 miles serve most half-marathon athletes well. Longer than 15 for a half is usually vanity, not fitness.
- Marathon training. This is where the long run earns its reputation. Ratio stays under 30%, but the absolute number climbs to 18 to 22 miles at peak. Not every week. Three or four long runs of 18 miles or longer across the build is the useful dose. Six or eight is how people arrive at the start line already tired.
- Ultra training. The ratio can break the 30% rule, but only if weekly volume is genuinely high and back-to-back long runs replace one enormous single. That is its own protocol, and outside the scope of this post.
The through-line: the long run's job is to build the aerobic base the race will draw from. That base is small for a 5K and most of the training for a marathon. The ratio holds either way.
The 22-mile ceiling, and why it exists
The marathon distance is 26.2 miles. Almost every training plan I have seen suggests peak long runs of 20, 22, sometimes 24. The evidence, and 15 years of coaching, points the same direction: the returns above 22 miles are small, and the recovery cost is large.
A 22-mile long run for a 4-hour marathoner takes roughly 3 hours 15 minutes at easy pace. Past that, the value is not fitness. It is fatigue rehearsal, and you can get that in a cheaper wrapper by finishing a shorter long run at goal marathon pace, or by stacking a Saturday medium-long with a moderate Sunday. Both cost less recovery than a 24-mile Sunday and both develop the specific quality the marathon actually tests, which is holding pace on tired legs.
For most marathoners: 22 miles or 3 hours, whichever hits first. A slower runner should not be out there for four and a half hours "just to prove they can." The cost, measured in the next ten days of training, is not worth the confidence bump on the day.
The exception is the experienced runner with several marathon blocks in the bank who runs faster paces. If a 22-mile long run takes them 2:20, adding a 26-mile progression run once in the block can pay off. That is a fine-tuning move, not a beginner one.
The pace of the long run: mostly boring, sometimes not
The most common way a long run breaks a week is not the distance. It is the pace. A long run run 20 seconds a mile too fast turns a stimulus into a race, and the next four days pay the bill.
The default: run 80 to 90% of your long run at easy pace, which is roughly 60 to 90 seconds per mile slower than your projected marathon pace. If your heart rate drifts above 75% of max on flat ground at that pace, you are already going too fast. Aerobic development happens at intensities you can hold without stress. Push, and you convert a base session into a partial workout that does neither job well. Why easy has to be actually easy covers the physiology in depth.
Once every two or three weeks, the long run becomes the workout. The two formats that pay:
- The progression long run. First 60 to 70% at easy pace, last 30 to 40% at goal marathon pace or slightly faster. Example: 16 miles with the last 5 at goal marathon pace. This builds the specific pace-on-tired-legs quality that decides the last 10K of the race.
- The steady long run. Whole run at "moderate" pace, roughly 30 to 45 seconds per mile slower than marathon pace. Useful earlier in the build to condition the aerobic system without the recovery cost of a progression.
Everything else, run genuinely easy. If you are not sure what any of these paces are, use one recent race to get a set of numbers rather than guessing at feel. The VDOT calculator turns a 5K time into a full training-pace set, and the VDOT explainer covers what to do with it.
How to build the long run week over week
Two rules, and they matter more than the peak number.
Rule one: add 1 to 2 miles at a time, not 3 or 4. A 10-mile long run to a 12-mile long run is a healthy step. A 10 to a 14 is a limp on Tuesday. Small steps stack; big steps blow up.
Rule two: hold every third week, do not climb every single week. A useful pattern for the long run is build, build, hold, build. Example: 12, 14, 14, 16, then 18, 18, 20, then 20, 22, 15 (cutback), 22. The hold weeks are where your body actually absorbs the load.
A representative long-run progression for a marathon build looks like this:
| Weeks out | Long run | Note |
|---|---|---|
| 18–15 | 10 → 14 mi | Base. All easy pace. |
| 14–11 | 14 → 18 mi | Start adding a steady middle. |
| 10–7 | 18 → 22 mi | One progression long run every two weeks. |
| 6–4 | 20, 22, 16 | Cutback in there. Peak, then absorb. |
| 3–1 (taper) | 14 → 10 → 6 mi | See the taper protocol. |
Specifics move athlete to athlete. The shape stays.
The pattern I watch for
About seven out of ten intermediate runners I take on have the same signature going in. Their long run is doing 40 to 50% of their weekly volume, they are running it 15 seconds a mile too fast, and they are wondering why their Tuesday workouts fell off a cliff two months ago.
The fix is not more discipline. The fix is a smaller long run and more midweek volume. When we cut a 16-mile Sunday down to 13 and add two miles to Wednesday, the ratio drops back into the healthy range, the Tuesday session comes back, and the long run stops being the sole aerobic input for the week. Six weeks later, the long run climbs to 16 again, but now it is 27% of a 60-mile week instead of 45% of a 35-mile week. Same run, different training.
The other pattern, less common, is the runner who caps their long run at 12 miles for a marathon because "that is what my old plan said." You can finish on that, but not run well. If the goal is a specific time, the long run has to stretch far enough that the last 10K of the race is a familiar body state. That is what 18 to 22-mile long runs are for.
One more note. Any long run over 90 minutes is also a fueling rehearsal. Same gels, same timing, same drink you will use on race day. Your gut is trainable and it needs the reps as much as your legs do. The gel protocol covers the specifics.
The protocol, in six lines
Hold your long run to 20 to 30% of weekly mileage. Cap it at 22 miles or 3 hours. Build it 1 to 2 miles at a time, hold every third week. Run 80 to 90% of it genuinely easy, with a progression finish once every two or three weeks. Practice fueling on every long run over 90 minutes. If the ratio is off, the whole week feels off, and the long run is the thing to shrink first.
If any of that is fuzzy for the race you are training for, the honest answer is to stop guessing. A long run written in isolation from the rest of your week is a guess. A long run written as part of a plan that reads your last long run, your sleep, and your Tuesday workout is a decision. That is the difference between a template and coaching.
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Written by
2:12 marathoner. 4× US Olympic Marathon Trials qualifier. 4× NCAA national champion and 4× NCAA runner-up. Spoke at the RRCA National Convention. Founder and head coach at RunFitCoach, where he coaches every athlete personally.