Marathon Time Predictor
Predict your marathon finish time from a recent 5K, 10K, or half marathon result. Three formulas, a training readiness modifier, and prediction tables.
Predict Your Marathon Time
Enter a recent race result at any distance
Predicted Marathon Times
Enter a race result above to see your predicted marathon times
Which Prediction Should You Trust?
Riegel Formula
Trust it if you are an experienced marathoner who has run 40+ miles per week consistently. The Riegel formula assumes you can maintain the same relative physiological effort across distances. For well-trained runners with good marathon-specific endurance, it is surprisingly accurate.
Best for: experienced runners, high mileage, flat courses
Cameron Formula
Trust it for your first or second marathon. Cameron adds a distance-based correction factor that accounts for the disproportionate difficulty of the marathon. It produces slower predictions than Riegel, especially when predicting from short distances like 5K. Most first-time marathoners find their actual time falls close to the Cameron prediction.
Best for: first-time marathoners, predictions from 5K or 10K
Adjusted Riegel (+6% Wall Effect)
Trust it if you are concerned about the wall or have limited marathon training. The 6% addition accounts for the glycogen depletion that happens around mile 18 to 20 in runners who are not specifically trained for the marathon distance. If your longest training run is under 18 miles, this is probably the most realistic prediction.
Best for: under-trained runners, first marathons, hilly courses
Half Marathon to Marathon Prediction Table
This table shows predicted marathon times for common half marathon finish times using all three formulas. Find your half marathon time and see the range of marathon predictions.
Why Marathon Predictions Are Harder Than Shorter Races
Predicting a 10K from a 5K is relatively straightforward because both distances rely on similar energy systems. The marathon is a different animal. Here are the specific factors that make marathon predictions unreliable compared to shorter distances.
Glycogen depletion (the wall)
Your body stores about 2,000 calories of glycogen (carbohydrate fuel) in muscles and liver. A marathon burns approximately 2,600 to 3,000 calories. Around mile 18 to 20, your glycogen runs out and your body shifts to burning fat, which produces energy 30 to 40 percent slower. This does not happen in a 5K, 10K, or even a half marathon. No prediction formula can perfectly model when and how hard the wall will hit you.
Muscle damage accumulates over distance
Every foot strike generates impact forces of 2 to 3 times your body weight. Over 26.2 miles, that adds up to tens of thousands of impacts. By mile 20, the micro-damage to your leg muscles causes a measurable loss of force production. Your legs literally cannot push off the ground as powerfully, regardless of your cardiovascular fitness. Shorter races do not produce this level of damage.
Mental fatigue compounds physical fatigue
Running for 3 to 5 hours requires sustained mental focus that shorter races do not demand. Decision fatigue, pain management, and motivation all become factors after hour two. Many runners slow down in the final miles not because their body cannot go faster, but because their brain is signaling them to stop.
Weather and hydration have outsized effects
A warm day that barely affects your 5K can cost you 10 to 20 minutes in a marathon. Dehydration that is negligible over 30 minutes becomes performance-limiting over 3 to 4 hours. Your longer exposure to conditions means small environmental factors compound into major performance impacts.
Training specificity matters more
You can run a decent 5K on general fitness alone. A marathon demands specific long-run endurance that takes months to build. Two runners with identical 5K times but different training backgrounds can finish a marathon 30 to 60 minutes apart. Weekly mileage, long run distance, and the number of months in training all influence the marathon more than the 5K.
Every Training Mile Matters
Marathon predictions improve when your mileage goes up. Motera makes every training run rewarding by turning your miles into captured territory. Your 20-mile long runs will paint massive sections of the map. Watch your city transform as you build the fitness to beat your predicted time.
MoteraFrequently Asked Questions
How accurate are marathon time predictions?
Marathon predictions from shorter races are generally within 5 to 10 percent for well-trained runners. Predictions from a half marathon are the most accurate because the distance is closest to the full marathon. Predictions from a 5K are least accurate because the physiological demands are very different. The Riegel formula tends to be 3 to 5 percent optimistic for marathons, which is why we include the Cameron and adjusted formulas.
Which prediction formula should I trust?
For your first marathon, trust the Cameron formula or the adjusted Riegel. The standard Riegel formula assumes you can maintain the same relative effort over the marathon distance, but most first-time marathoners slow down significantly after mile 18 to 20. The Cameron formula accounts for this distance-specific fatigue. If you are an experienced marathoner with 40+ miles per week in training, the standard Riegel is closer to reality.
Can I predict my marathon time from a 5K?
You can, but the prediction will be less reliable than one from a 10K or half marathon. A 5K tests your VO2max and anaerobic capacity more than your endurance. The marathon, by contrast, is almost entirely an aerobic endurance event. A 20-minute 5K runner could finish a marathon anywhere from 3:30 to 4:15 depending on their endurance training and marathon experience.
Why does weekly mileage affect marathon predictions?
Weekly mileage is the strongest predictor of marathon success. Runners who average fewer than 30 miles per week typically lack the aerobic endurance to hold their predicted pace for the full 26.2 miles. The "wall" at mile 18 to 20 hits harder when you have not built a deep endurance base. Higher mileage runners have more mitochondria, better fat oxidation, and more resilient muscles.
How do I use my half marathon time to predict a marathon?
Enter your half marathon time in the calculator above and select "Half Marathon" as the distance. The three formulas will give you a range of marathon predictions. A common rule of thumb is to double your half marathon time and add 10 to 20 minutes. For a 1:45 half marathon, that gives a range of 3:40 to 3:50. The calculator on this page uses more precise mathematical formulas.
What is the Riegel formula?
The Riegel formula predicts race time as: T2 = T1 x (D2 / D1) ^ 1.06. T1 is your known race time, D1 is the known distance, D2 is the target distance, and the exponent 1.06 accounts for the fact that pace slows as distance increases. Created by Pete Riegel in 1977, it remains one of the most widely used prediction formulas in running.
What is the Cameron formula?
The Cameron formula is a modification that accounts for the disproportionate difficulty of longer distances. It uses a variable correction factor that increases with the distance gap between your known race and the target race. For short-to-marathon predictions (like 5K to marathon), Cameron produces significantly slower and more realistic times than Riegel.
Should I adjust my prediction based on course elevation?
Yes. These predictions assume a flat course. For every 100 feet (30 meters) of net elevation gain in a marathon, add roughly 1 to 2 minutes to your predicted time. A hilly course like Boston (which has a net downhill but significant mid-race hills) can add 5 to 10 minutes compared to a flat course like Berlin or Chicago.
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