How Long Should Your Long Run Be?

Ask any first-time marathoner what they're nervous about and you'll hear it: "I need to do a 20-miler." The 20-mile long run has become marathon training's sacred cow. But here's the uncomfortable truth: there's nothing magical about 20 miles. It's a round number that stuck. What actually matters is finding the long run distance that builds fitness without breaking you down.

The Purpose of the Long Run

Long runs build aerobic capacity, teach your body to burn fat efficiently, strengthen connective tissue, and develop the mental resilience needed for racing. These adaptations happen gradually with consistent training.

The key word is consistent. A long run that leaves you wrecked for four days isn't building fitness-it's just creating fatigue that undermines the rest of your training.

Where Diminishing Returns Begin

At some point, extending your long run delivers diminishing returns-the recovery cost exceeds the fitness benefit. Research and coaching experience suggest benefits begin to plateau around certain time thresholds:

Beyond these durations, you're still getting some benefit, but the cost-benefit ratio shifts unfavorably. A 3.5-hour long run isn't 17% better than a 3-hour run-but it might require 50% more recovery.

Why Time Matters More Than Distance

A 7:30/mile runner covers 20 miles in 2:30. A 12:00/mile runner takes 4 hours for the same distance. The physiological stress of those two runs is vastly different-yet both runners "did their 20-miler."

This is why time-based caps often make more sense than distance targets. The stress of running is largely a function of duration, not miles covered.

If your easy pace means 20 miles takes 4+ hours, you're likely better served by a 2:45-3:00 long run-whatever distance that covers.

Where the 20-Mile Standard Came From

The 20-mile long run became gospel through popular beginner marathon programs, particularly Hal Higdon's widely-used training plans. These programs democratized marathon training, making the distance accessible to millions of recreational runners.

And they worked. But somewhere along the way, "20 miles" transformed from "a reasonable peak long run for this program" into "the number you must hit or you'll fail."

The truth: 20 miles was never based on research showing it's superior to 18 or 22 miles. It's close enough to marathon distance to feel like adequate preparation, far enough to leave something for race day. A sensible heuristic-not a physiological threshold.

The Math Problem with Chasing 20 Miles

When runners fixate on hitting 20 miles, they often ignore what actually matters: how that long run fits into their overall training.

For most recreational marathoners running 30-45 miles per week, a 20-mile long run creates a massive spike in training stress. The recovery cost is high, often compromising the quality of training in the days that follow.

This is how injuries happen. Not from running marathons, but from forcing long runs that your weekly volume can't support.

What Actually Matters for Race Preparation

Coaches and exercise scientists generally agree on what predicts success:

• Consistency over 12-16 weeks: Showing up day after day matters more than any single workout.
• Total weekly volume: The sum of all your running, not just the long run.
• Arrival at the start line healthy: You can't race well if you're injured or overtrained.
• Race-specific work: Tempo runs, marathon pace work, and progressive long runs.
• Adequate recovery: Adaptations happen during rest, not during the runs themselves.

Notice what's not on the list: hitting exactly 20 miles.

The Hansons Approach: 16 Miles Is Enough

The Hansons Marathon Method is perhaps the most prominent training philosophy that explicitly rejects the 20-mile dogma. Their longest run caps at 16 miles-and it's produced thousands of successful marathons, including many Boston qualifiers.

Their reasoning:

• Cumulative fatigue: Running 16 miles on legs already tired from the week's training simulates late-race conditions better than a single fresh 20-miler.
• Sustainable training: Shorter long runs allow runners to recover adequately and complete quality sessions throughout the week.
• Consistency wins: Ten solid 16-mile long runs beats three 20-milers that leave you wrecked.

The Hansons approach isn't "easier"-their weekly volume is substantial. But it demonstrates that marathon success doesn't require chasing arbitrary distance milestones.

Signs Your Long Run Is Too Long

• Multi-day recovery: If you need more than 48 hours to feel normal, the run may be too demanding.
• Compromised quality sessions: Your Tuesday workout shouldn't suffer because of Sunday's long run.
• Accumulated fatigue: Feeling progressively more tired over weeks suggests overall training load is too high.
• Dread: If you're anxious about every long run due to its length, that's a signal.
• Injury patterns: Overuse injuries often correlate with long run volume that exceeds your durability.

When Longer Long Runs Make Sense

This isn't an argument against ever running 20 miles. For some runners, longer long runs are appropriate:

• High-mileage runners: If you're running 60-70+ mpw, an 18-22 mile long run fits within sustainable percentages.
• Experienced marathoners: Runners with many marathons behind them have developed durability that supports longer efforts.
• Specific race simulation: One or two longer runs late in a training cycle, done deliberately with adequate recovery planned.
• Ultra training: Where time on feet is the primary adaptation being sought.

The key is intentionality. A 20-mile run done because your base supports it is different from a 20-mile run done because "you have to."

Finding Your Sweet Spot

The ideal long run length depends on:

• Weekly mileage: Long runs typically work best at 20–30% of weekly volume
• Experience: Newer runners often benefit from more conservative long runs
• Pace: Slower runners should use time caps rather than distance targets
• Recovery capacity: This varies by age, sleep, stress, and individual physiology

Better Questions Than "How Long?"

Instead of asking "How do I fit in a 20-miler?", try these questions:

• What's my total weekly mileage, and what long run fits sustainably within it?
• How am I recovering from my current long runs? Can I handle more, or am I already at my limit?
• What's the purpose of this long run-aerobic base, race simulation, mental confidence?
• Would building weekly mileage serve me better than extending my longest run?

The Bottom Line

You don't need to run 20 miles to finish a marathon. You don't need to run 20 miles to run a good marathon. What you need is consistent training, adequate volume, and arriving at the start line healthy and prepared.

If your training supports 20-mile long runs, great-do them. If it doesn't, do the long runs your weekly mileage can sustain and trust the process. The marathon rewards consistency, not single heroic efforts.

Long runs are essential, but they're one piece of a larger training puzzle. The goal isn't to survive the longest possible long run-it's to find a sustainable duration that builds fitness without compromising the rest of your training.

When in doubt, err on the side of slightly shorter. You can always build. You can't un-injure yourself or un-burn out.

Twenty miles isn't magic. It's just a number.

Related