Every marathon, thousands of runners toe the start line knowing they might not make the finish. Some get pulled by medical staff. Some hit the wall and walk off course. Some realize at mile 18 that today isn't their day.
But how common is it to DNF a marathon? We dug into the data from major marathons worldwide to find out.
Key Takeaway
The average marathon DNF rate is 1–2% at major city marathons under normal conditions. But this number hides enormous variation: hot-weather races can see DNF rates of 5–10%, and ultramarathons routinely exceed 20–30%. First-time marathoners DNF at roughly 2x the rate of experienced runners.
Overall Marathon DNF Rates
Across major marathons, DNF rates are surprisingly low — but not as low as you might think:
| Marathon | Typical DNF Rate | Notable High Year |
|---|---|---|
| Berlin | 1.0–1.5% | 2.1% (warm 2018) |
| London | 1.0–1.5% | 2.3% (warm 2018) |
| New York City | 1.0–2.0% | 2.5% (wind/cold years) |
| Chicago | 1.5–2.5% | 5.8% (2007, 31°C/88°F) |
| Boston | 1.5–3.0% | 5.2% (2012, 27°C/81°F) |
| Tokyo | 0.8–1.5% | 1.8% (humidity) |
| Marine Corps (DC) | 2.0–3.5% | 4.1% (heat years) |
| Los Angeles | 2.5–4.0% | 5.5% (sun exposure) |
Berlin and Tokyo have the lowest DNF rates — both are fast, flat courses with cool race-day temperatures. Boston and LA have the highest among major marathons, driven by heat risk and course difficulty respectively.
These DNF rates include all athletes who started but did not receive an official finish time. This encompasses medical withdrawals, voluntary stops, and runners who miss time cutoffs. It does NOT include DNS (Did Not Start) — runners who registered but never showed up.
When Do Runners DNF?
The marathon has a predictable dropout pattern. Analysis of timing mat data shows where runners leave the course:
| Race Segment | % of All DNFs | Why |
|---|---|---|
| 0–10 km | 5–8% | Early injury, equipment issues |
| 10–21 km | 10–15% | Pacing mistakes become apparent |
| 21–30 km (half to 30K) | 20–25% | Glycogen depletion begins |
| 30–35 km | 30–35% | "The Wall" — peak dropout zone |
| 35–42 km | 15–20% | Late-stage collapse, time cutoffs |
The 30–35 km segment is where marathons are lost. This is the infamous "wall" — the point where glycogen stores are depleted and the body shifts to fat oxidation, which is dramatically slower.
Approximately 30–35% of all DNFs occur in this 5 km stretch, making it the single most dangerous section of the race by dropout rate.
The Physiology of the Wall
The wall isn't just psychological. At marathon effort:
- The body stores approximately 2,000 calories of glycogen
- Marathon running burns approximately 70–100 calories per km
- At 30 km, most runners have exhausted glycogen reserves
- The shift to fat metabolism causes a 10–20% drop in available power output
- Runners who went out too fast hit the wall earlier and harder
Weather: The Single Biggest DNF Factor
No variable predicts marathon DNF rates better than temperature:
| Temperature Range | Typical DNF Rate | Impact |
|---|---|---|
| 5–10°C (41–50°F) | 0.8–1.5% | Ideal conditions |
| 10–15°C (50–59°F) | 1.0–2.0% | Still favorable |
| 15–20°C (59–68°F) | 2.0–3.5% | Noticeable increase |
| 20–25°C (68–77°F) | 3.5–6.0% | Significant risk |
| 25°C+ (77°F+) | 5.0–10%+ | High-risk conditions |
Case Studies: Heat Disasters
Chicago 2007 — Race-day temperatures reached 31°C (88°F) with high humidity. The DNF rate hit 5.8%, the race was shortened for slower runners, and one runner died. Over 300 runners were taken to hospitals.
Boston 2012 — Temperatures reached 27°C (81°F), unusual for April in New England. The DNF rate jumped to 5.2%, nearly triple the normal rate. The BAA offered deferrals to registered runners before the race.
London 2018 — The hottest London Marathon on record at 24°C (75°F) produced a 2.3% DNF rate — modest by absolute standards but 50% higher than the typical year.
Key Takeaway
For every 5°C increase above 15°C, DNF rates roughly double. Heat doesn't just slow runners — it removes them from the race entirely. If you're racing a warm marathon, adjust your goal time by 1–2 minutes per degree above 15°C, or risk being a statistic.
DNF Rates by Gender
The data on gender and DNFs shows a consistent pattern:
| Gender | Average DNF Rate | Notes |
|---|---|---|
| Men | 2.0–2.5% | Higher ego-driven pacing errors |
| Women | 1.0–1.5% | More conservative early pacing |
Men DNF at roughly 1.5–2x the rate of women across most major marathons. The primary explanation supported by pacing data:
- Men are more likely to positive-split. They go out faster relative to their fitness and pay for it later.
- Men are more likely to race above their ability. Men more frequently attempt goal paces that exceed their training level.
- Women pace more conservatively. Studies show women slow down less in the second half, reducing the risk of catastrophic bonking.
A study published in PLOS ONE analyzing over 91,000 marathon results found that men slowed by an average of 15.6% in the second half, while women slowed by only 11.7%. The more aggressive the positive split, the higher the DNF risk.
DNF Rates by Experience
First-time marathoners face significantly higher DNF risk:
| Experience | DNF Rate | Primary Causes |
|---|---|---|
| First marathon | 2.5–4.0% | Under-training, pacing errors, mental |
| 2–5 marathons | 1.5–2.0% | Improved pacing, training knowledge |
| 6–10 marathons | 1.0–1.5% | Course management, nutrition strategy |
| 10+ marathons | 0.5–1.0% | Deep experience, conservative targets |
The biggest improvement comes between the first and second marathon — simply having experienced the wall once makes an athlete dramatically better at managing it.
DNF Rates by Pace Group
Slower runners DNF at higher rates, but not for the reasons you'd expect:
| Target Pace | DNF Rate | Main Risk |
|---|---|---|
| Sub-3:00 | 0.5–1.0% | Injury (over-racing) |
| 3:00–3:30 | 1.0–1.5% | Pacing collapse |
| 3:30–4:00 | 1.5–2.5% | Glycogen depletion |
| 4:00–4:30 | 2.0–3.0% | Under-training |
| 4:30–5:00 | 2.5–4.0% | Time cutoff + fatigue |
| 5:00+ | 3.0–6.0% | Time cutoff, walking |
Sub-3:00 runners have the lowest DNF rate despite running the hardest effort. They're typically the most trained, most experienced, and most disciplined about nutrition and pacing.
The highest DNF rates are in the 5:00+ group, where athletes face a dual threat: accumulated fatigue over 5+ hours AND approaching course time cutoffs (typically 6–7 hours).
Time Cutoffs and Forced DNFs
Every major marathon has a course time limit. Runners who don't reach certain checkpoints are pulled off the course:
| Marathon | Time Limit | Checkpoint Enforcement |
|---|---|---|
| Boston | 6:00:00 | Rolling cutoffs every 5K |
| New York City | Unofficial ~7:30 | Lenient, sweep buses |
| Chicago | 6:30:00 | Checkpoint cutoffs at 20 mi |
| London | 8:00:00 | Very lenient |
| Berlin | 6:15:00 | Moderate enforcement |
| Tokyo | 7:00:00 | Strict checkpoint cutoffs |
An estimated 0.5–1.0% of all marathon DNFs are forced — runners who were still moving but missed a checkpoint cutoff. This disproportionately affects runners in the 5:30–6:30 pace range.
Ultra-Marathon DNF Rates: A Different World
For comparison, ultramarathon DNF rates make marathon numbers look trivial:
| Distance | Typical DNF Rate |
|---|---|
| 50K | 5–10% |
| 50 mile | 10–20% |
| 100K | 15–25% |
| 100 mile | 25–40% |
| Multi-day | 30–50% |
The Western States 100-Mile Endurance Run averages a 35–40% DNF rate. The Barkley Marathons, an extreme 100-mile race, has a completion rate of less than 2% — most years, nobody finishes.
Medical DNFs: When the Body Shuts Down
Medical DNFs account for approximately 30–40% of all marathon dropouts:
| Condition | % of Medical DNFs | Severity |
|---|---|---|
| Hyponatremia (low sodium) | 10–15% | Can be fatal |
| Hyperthermia (overheating) | 20–25% | Requires immediate cooling |
| Musculoskeletal injury | 30–35% | Knee, ankle, hip |
| Gastrointestinal distress | 15–20% | Dehydration, vomiting |
| Cardiac events | 1–3% | Rare but serious |
| Exhaustion/collapse | 10–15% | Post-finish line collapse common |
The marathon has a cardiac death rate of approximately 1 per 50,000–100,000 finishers, based on large-scale epidemiological studies. While tragic when it occurs, this rate is comparable to the background risk of vigorous exercise in the general population.
How to Avoid Becoming a DNF Statistic
Based on the data, the factors most strongly associated with finishing are:
1. Train Enough Volume
Runners who complete at least 3 runs of 30+ km in training have a DNF rate under 1%. Runners who never exceed 25 km in training have DNF rates of 5%+.
2. Respect the Weather
If race day is warm, adjust your goal pace immediately. A 4:00 finish in 10°C conditions becomes a 4:15–4:20 in 25°C. Accept it or risk dropping.
3. Pace Conservatively
Start at your target pace or slightly slower. The data is unambiguous: positive splitting (going out faster than you finish) is the strongest predictor of DNF risk. Negative splitting is nearly insurance against dropping.
4. Nail Your Nutrition
Practice race-day nutrition in training. Take gels or carbs every 30–45 minutes starting at 45 minutes. Don't try anything new on race day.
5. Have a Walk-Run Strategy Ready
If you hit the wall, switching to run-walk intervals (e.g., run 4 minutes, walk 1 minute) is dramatically better than stopping entirely. Most DNFs happen when runners stop and can't restart.
Related Articles:
- Marathon Positive Split Data — Why most runners slow down and what the data shows
- What Is a Good Marathon Time? — Percentiles and targets by age
- Marathon Training Volume: What the Data Shows — How much training is enough?
Tools:
- Percentile Calculator — See where your finish time ranks