The most common question I get from beginning marathoners is some version of: ‘How long should my longest long run be?’
The answer? Well, I’ll just put on my lawyer hat and give the answer we lawyers are trained to give: it depends.
I know this isn’t terribly helpful, but the answer is there is no ‘right’ answer.
The Longest Long Run
There are many schools of thought on how long the longest marathon training long run should be.
Some plans and coaches say 20 miles, others 26.
There are some lower-mileage plans that top out at 16 miles.
Some coaches suggest looking to time on your feet instead of distance. Suggesting your longest run should be 3 hours, regardless of how much distance you’ve covered.
Some say time on your feet equivalent to your goal race time.
Other plans suggest doing shorter long runs, but done at a pace closer to your race pace than the usual long run pace.
This will either make you feel much better or much worse, but there is no commonly accepted scientific basis for one approach being better than the others.
Factors to Consider
One main purpose of the marathon training long run is to build endurance. However, physical endurance is only part of the long run equation.
Your mind, your stomach and your bowels all need practice too.
Depending on which parts of you need more practice (and what need more rest), your longest long run distance should vary.
Some questions to ask yourself and things to consider:
Training Plan Mileage
What does your training plan look like? How many miles a week are you running?
The common wisdom is your long run shouldn’t be more than 50% of your total weekly mileage. While your long run is one of the most important runs you do during marathon training, make sure it isn’t a disproportionate amount of your overall mileage.
Training Plan Methodology
Is there an overall training methodology to your training plan?
One well-known training plan with a very specific methodology is Hansons, which results in an overall lower-mileage (but higher intensity) training plan.
Hansons’ long runs are in the 16-18 mile range, but doing these shorter distance long runs outside of that specific training plan wouldn’t have the same effect since you’d be missing the other parts of their training puzzle.
What Other Training Do You Need?
Consider where you have struggled in your training and in your long runs.
Do you consistently not fuel sufficiently or struggle with mindset issues?
Have you had gear issues when you get into longer distances?
In these cases, consider long runs on the longer side, so you can work on the ‘mushier’ aspects of the long run.
Your History With Injury
If you have a history of recurring injury, first and foremost, consult with your doctor to get their advice on your running and marathon training.
After you’ve gotten an all clear to run and marathon train, focusing more on time on your feet – which usually results in shorter runs – may be a better approach and can be less traumatic for your body.
Long Run Route
Consider where you will be running your long runs.
If your long run route is super hilly or will be otherwise physically challenging, looking to time instead of distance can be a more accurate reflection of your effort.
What Is Your Experience With Marathons?
If you are training for your first marathon, your goal may just be to finish. In this case, a good approach to training is to do just enough, but not too much.
If your goal is just to finish, consider erring on the shorter side (within reason).
However, if you’ve done several marathons and have a specific time goal, you become more able, and it becomes more important, to push long run distances or paces, focusing on making your long runs closer to marathon pace.
No Really, How Long Should I Run?
I’ll admit to my bias: I fall squarely into the 20 miles as the longest long run camp. It’s what I use personally when training for a marathon, and barring specific reasons to change it up, it’s what I assign to my coaching clients.
While 20 miles is my go-to and is the most common longest long run distance for off-the-shelf training plans, there is no proof that 20 mile long run marathon trainees are more prepared than runners who, for example, train in the metric system and top out at 30 or 35K (18-21 miles).
Pro 20 Miles
Admittedly, 20 miles is arbitrary. There is nothing special about a 20 mile long run. It doesn’t unlock any special marathon secrets or abilities.
There is a huge mental benefit to hitting a distance in training where the distance starts with a 2. It is a major milestone for many first-time marathon trainees.
In the same way that something costing $19.99 feels way cheaper than something costing $20.00, 20 miles feels much longer than 19.
Plenty Of Time On Your Feet
20 miles gives all runners sufficient time on your feet training and ample time to test out fueling options and address other long run issues.
And, if you pace it right, a 20 mile long run, at your long run pace, should be pretty close to the time you’ll be running on race day.
To do the (very rough) math: Imagine your race day goal pace is 10:15 (roughly a 4:30 hour marathon). Your long run pace should be about 60-90 seconds slower than your predicted race pace.
In that case, a 20-mile long run, running at an 11:45 pace, would have you running about 4 hours.
It’s not exact, but pretty close.
Cons 20 Mile
Some studies show that the most physical gains come in the first 2 hours of a run. After about 3 hours, the risks of injury and over-training sharply increase.
I don’t want to minimize these concerns, long runs are hard on the body and the risks of injury or over-training are very real.
But it’s important to note that in the studies I’m aware of, the test subjects are always experienced runners, veteran marathoners and usually have marathon finish times in the 3-3:30 hour range.
For slower runners, 3 hours just isn’t enough time for the other long run benefits (like fueling and mindset) to develop since it’s a much smaller percentage of the time you’ll be running on race day.
What To Do
Ideally, work with a coach and develop a plan (and long run distance) that is right for you, your physiology, and your training goals.
Whatever your longest long run distance is, it’s important to increase both your long run and weekly mileage totals slowly.
Whether your longest run is 18, 20, 22, or 26 miles, that should be months into training, after slowly building up to that distance week after week after week.