How Far Should You Run Before a Marathon?

Marathon training has many nuances, but one of the most common questions is also one of the most basic. How far should you run before a marathon? What’s the longest long run you need to do in order to finish, PR, or qualify for Boston?

If you look at popular training methods, you will receive answers ranging from 16 miles (Hansons) to 26 miles (Galloway). Other plans follow the framework that a long run should not comprise more than 25% of the overall weekly mileage nor exceed three hours in duration. The wide array of answers can be overwhelming and confusing.

The truth is, the answer is not the same for every runner. These are some factors to consider when determining how far you should run before a marathon.

This post talks about the longest long run of training. This does not mean that every long run should be this length! You want to gradually increase your mileage, add in variety, incorporate cutback weeks, and include an appropriate taper.

Consider Time on Feet, Not Distance

The marathon is 26.2 miles regardless of how fast you run. However, the training of a 3:00-3:30 marathoner will look much than the training of a 5+ hour marathoner. Several factors differentiate their training, but one of the biggest differences will be the long run.

A 5 hour marathoner will take longer to run 20 miles than a 3:30 marathoner. Yes, the 5 hour marathoner will have to prepare for more time on their feet on race day. However, a point of diminishing returns exists; too long of a long run will increase injury risk and include recovery so long that it interferes with the next week of training.

The exact duration of the longest long run during marathon training depends on your anticipated finish time. A 3:30 marathoner needs to prepare for 3.5 hours on their feet. A long run of 3-3.5 hours is both practical and safe (although be sure to consider the factors below) – roughly 20-22 miles. No need exists for the 3:30 marathoner to run for four hours in the long run.

However, a 5:00+ marathoner needs to prepare for time on their feet and will likely complete 4 to 4.5 hour long runs. They might cover 18 miles or 19 miles total in this time. It is not recommended to run for longer than 4.5 hours due to the prolonged recovery period and increase the risk of injury.

For more on the difference in long run training times, reference this article from Greg McMillan. The advice is practical to the average marathoner and scientifically sound.

Consider Injury Risk

We could try to break down all the reasons why, but one of the most basic variations between individual runners is that some are prone to injury and others are not. Some runners can make all sorts of training errors and cross the finish line of their marathon injury-free. Others endure injury in marathon training no matter what precautions they take.

Know your recovery rate and what increases your risk of injury. If long runs leave you sore for days and you frequently are injured during marathon training, be cautious about your longest long run.

Consider Runner’s Background and Strengths

Everything from muscle fiber composition to training background (which can, over time, alter your muscle fiber types!) to even personal preference determines a runner’s strengths. Some runners have a propensity to endurance, others excel at speed, and then many runners are in the middle.

On one extreme, the endurance runner recovers quickly from long runs and typically has higher fatigue resistance (doesn’t fade during the run). These runners can often handle long runs of 20-22 miles with relative ease – and they can handle more runs at this distance in training.

The speed-based runner, on the end of the spectrum, struggles with the slow pacing and duration long runs and takes longer to recover from them. These runners may benefit more from “shorter” long runs. For example, a 4-hour marathoner who is speed-based might only do 3 hours (18-19 miles).

Again, many runners fall in the middle, but it is worth knowing how your body handles long runs when you are deciding how far you will run before a marathon.

Consider Goals

Let’s take two runners: one wants to finish their first marathon, the other wants to qualify for Boston. The first time marathoner runs an average of 15-18 miles per week, with their longest run before marathon training of 6 miles. The BQ hopeful runs an average of 35-40 miles per week and their long run (when not training for a race) is 10-12 miles. A good coach simply would not prescribe two 20-milers to both of these runners.

For the first-time marathoner, the longest run might be 18 miles. This is enough time on the feet, especially at a slower pace, to prepare a novice for the marathon distance. This hypothetical runner can build up gradually to 18 miles, including adaptation weeks and cutback weeks.

The BQ marathoner will do one 22 miler and two to three 20 milers (including one with marathon pace) before their race. This runner has completed marathons before and is adapted to marathon long runs. Since their goals are bigger – a challenging time goal, versus just finishing – the training stimulus must be appropriately higher. The more experienced a marathoner is, the more stimulus they need as well to prevent plateauing.

Is there a minimum distance for the longest long run?

The marathon is physically demanding; if you can, you should try to do the appropriate amount of training. However, life happens: you might get sick, work might demand more of your time, family concerns may arise, or you might sustain an injury.

From my experience of coaching runners, sixteen miles is the minimum I would recommend. However, this distance should be attained through a gradual increase in mileage. Do not jump into a 16 miler if your most recent long run was significantly shorter. 

No marathon is ever worth injury. If you have not appropriately built up your long runs, consider deferring the race or switching to a shorter distance.

If you are working with a coach, talk to them about your unique situation. Generalized advice will be more cautious, while a coach understanding your strengths, weaknesses, injury risk, and training situation can provide a more nuanced solution.

Ultimately, there is no concrete prescription as to exactly how far you should run before a marathon. The exact answer will vary based on the individual runner. Even for the individual, the answer will change as they progress in the sport.

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