How Far Should You Run Before a Marathon? The Answer Might Surprise You

If you’re training for a marathon, one of the most common (and important) questions you’ll face is: How far should my longest run be before race day?

Scroll through training plans, and you’ll see answers ranging from 16 miles to the full 26.2. That’s a wide spread.

Some methods like the Hansons plan cap the long run at 16 miles.

Others, like Galloway’s, take you all the way to marathon distance. Still others say your long run should never exceed 25% of your weekly mileage or more than three hours total.

Confused yet?

Totally understandable. The truth is, there’s no one-size-fits-all answer.

The ideal distance for your longest long run depends on several key factors, from your goal finish time to your injury history.

Let’s break it down.

1. Focus on Time on Feet, Not Just Distance

Whether you're running a 3:30 or a 5:30 marathon, the distance is the same, but your time on feet varies drastically.

That’s why it’s smarter to plan long runs based on duration, not just mileage.

• A 3:30 marathoner is preparing for 3.5 hours of running. Their longest run will typically be around 20–22 miles, or 3 to 3.5 hours. Pushing to 4 hours isn't necessary and may even be counterproductive.
• A 5:00+ marathoner needs more endurance time. They may run for 4 to 4.5 hours, covering 18–19 miles. Going beyond 4.5 hours? That’s usually not advised, as recovery demands and injury risks increase significantly.

Keep in mind: this is your longest long run. You’ll build up to it gradually and only do it once, likely 3–5 weeks before race day.

2. Factor in Injury Risk

Every runner’s body is different. Some can train hard without issue; others seem to get injured no matter how cautiously they train.

If you know that long runs leave you feeling beat up or if you have a history of injury during marathon training it's smart to scale back. Prioritize consistency and smart progression over mileage bragging rights.

If you’re sore for days after every long run, or if recovery spills over into the following week’s training, that’s a red flag.

3. Know Your Strengths as a Runner

Your personal physiology plays a role, too.

• Endurance-oriented runners (think: high fatigue resistance, quicker recovery) often handle 20+ mile long runs well and can do more of them during a cycle.
• Speed-based runners, on the other hand, often struggle more with slower, longer sessions. They may benefit from slightly shorter long runs, even if their goal time is aggressive.

Not sure where you fall? Think about how you feel during and after long runs. Do you bounce back quickly, or do you feel wiped out for days?

4. Align With Your Goal

Your training should reflect your marathon goals.

• First-time marathoners aiming to finish safely, especially those running low mileage overall, might peak with a long run of 16–18 miles. That’s usually enough to prep the body for race day without overdoing it.

• Boston hopefuls or PR chasers? That’s a different story. These runners often log multiple 20-milers, with at least one going up to 22 miles, sometimes with stretches at marathon pace.

Bottom line: your training volume, experience, and goals all matter when deciding how far to go.

What About the Minimum?

In general, 16 miles is the shortest distance most experienced coaches recommend for a longest long run.

But don’t leap into a 16-miler if your previous longest run was 10 miles. Gradual progression is key.

Life happens: illness, work stress, injuries and sometimes training gets interrupted. If you’re unable to build up safely to at least a 16-mile run, consider adjusting your race plan or deferring.

Final Thoughts: It’s Not About One Magic Number

Marathon training is not a checklist. The perfect long run distance depends on your pace, experience, goals, and injury history.

There’s no single “correct” number. Even for the same runner, the right answer might change from one training cycle to the next.

If you’re working with a coach, lean on them to tailor your plan. If you’re self-coached, be honest with yourself about how your body is responding to the training load.

And remember: no marathon finish is worth an injury. Train smart, listen to your body, and adjust when needed.