Marathon Long Run Calculator

Find your ideal long run distance for marathon training. Based on proven coaching principles-not arbitrary rules.

Calculate Your Marathon Long Run

Enter your weekly mileage and pace to get a personalized recommendation. See exactly how your long run fits into your training.

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How Long Should Your Marathon Long Run Be?

The short answer: 20-30% of your weekly mileage, capped at about 3 hours. But the better answer depends on where you are in training and your weekly volume.

Here's what the research and coaching wisdom tell us:

  • Lower-mileage runners (30-40 mpw) can safely push to 30% for their long run-that's 9-12 miles
  • Moderate-mileage runners (40-55 mpw) typically stay around 25%-that's 10-14 miles
  • Higher-mileage runners (55+ mpw) often stay closer to 20%-but that's still 11-16 miles

The percentage approach is more useful than fixed distances because it accounts for your training capacity. A 20-mile run on 30 mpw (67% of volume) is much more stressful than a 20-mile run on 60 mpw (33%).

Why 20 Miles Isn't Magic

The 20-mile long run has become marathon training's sacred cow. But there's nothing special about that number-it's just a round figure that stuck in popular consciousness.

Consider:

  • The Hansons Marathon Method caps long runs at 16 miles
  • Many elite runners rarely exceed 2.5 hours regardless of pace
  • Jack Daniels recommends capping at 25% of weekly mileage or 2.5 hours
  • Pfitzinger's plans peak at 20-22 miles only for his highest-volume programs

What matters more than hitting a specific distance is consistency over time. Ten solid 16-mile long runs beat three heroic 20-milers that leave you injured or overtrained.

Marathon Long Run Guidelines

Time Caps

Most coaches recommend capping marathon long runs at 2.5-3 hours. Beyond this point:

  • Glycogen depletion becomes severe
  • Muscle damage increases disproportionately
  • Recovery time extends significantly
  • Injury risk spikes

Frequency

Peak-distance long runs shouldn't happen every week. A typical pattern:

  • Build week: Long run at target distance
  • Build week: Long run at target distance
  • Recovery week: Long run reduced by 20-30%
  • Repeat

Effort Level

Marathon long runs should be genuinely easy-1-2 minutes per mile slower than goal pace. Save the fast finishes for specific workouts, not your weekly default.

Ready to Calculate?

Get your personalized marathon long run recommendation based on your current training.

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Related Resources

→ How Long Should Your Long Run Be? The Complete Guide → Marathon Training Mileage: How Much and How to Build → Tapering Your Long Run: How to Peak for Race Day
"text": "Your marathon long run should typically be 20-30% of your weekly mileage, capped at about 20-22 miles or 3 hours. For a runner doing 50 miles per week, that's 10-15 miles. Most successful marathoners don't need runs longer than 20 miles."