Marathon Predictor
Free marathon time predictor and race time predictor. Predict marathon time from a recent 5K, 10K, or half marathon using Riegel, Cameron, and adjusted formulas. Predicts every distance from 1 mile to 50K.
Beat Your Predicted Times with Motera
The best way to improve your race predictions is to run consistently. Motera turns every run into a strategy game where you capture real-world territory, compete on leaderboards, and earn XP. When running feels like a game, you actually want to get out the door and train.
Download Motera FreeFrequently Asked Questions
How accurate is the Riegel formula for predicting race times?
The Riegel formula is remarkably accurate for distances between 5K and marathon, especially for trained runners. It tends to be most accurate when predicting times for distances close to your input race. For example, predicting a half marathon from a 10K result is generally more reliable than predicting a marathon from a 5K. Most runners find predictions within 2 to 5 percent of their actual times when properly trained.
What is the difference between the Riegel and Cameron formulas?
The Riegel formula uses a simple power law relationship (T2 = T1 * (D2/D1)^1.06) and works well for most recreational runners. The Cameron formula uses a more complex fatigue curve that accounts for how fatigue increases at different rates for different distances. Cameron tends to give slightly faster predictions for shorter races and slightly slower ones for ultra distances.
Can I predict a marathon time from a 5K result?
Yes, but with caveats. The larger the gap between your input distance and predicted distance, the less accurate the prediction. A 5K tests your speed and VO2max, while a marathon tests endurance and fuel management. Someone who is fast at 5K but has not done long run training may find their actual marathon time is slower than predicted. For best results, use a 10K or half marathon time to predict a marathon.
Why do the three formulas give different predictions?
Each formula models the relationship between distance and fatigue differently. The original Riegel uses an exponent of 1.06, the adjusted version uses 1.07 (slightly more conservative for longer distances), and Cameron uses a curve-based approach. The range between them gives you a realistic window of what to expect on race day.
Should I use my training pace or race pace for predictions?
Always use your best recent race time or a genuine all-out time trial effort. Training paces are typically 30 to 60 seconds per mile slower than race pace. Using a training pace will give you predictions that are too slow. If you have not raced recently, do a solo time trial at a local track or measured course and give maximum effort.
How recent should my input race time be?
Ideally within the last 3 months. Fitness changes over time, so an old PR may not reflect your current ability. If you have been training consistently and improving, your current fitness may actually be better than your most recent race suggests. If you have taken time off, your predictions may be optimistic.
What does the performance level rating mean?
The performance level gives you context for how your time compares to other runners. Elite means you are in the top 1 to 2 percent of all runners. Advanced puts you in the top 10 to 15 percent. Intermediate is the middle of the pack, and Beginner means you are in the early stages of your running journey. Every level is an achievement and a starting point for improvement.
Do these formulas work for ultramarathons?
The formulas become less reliable beyond marathon distance because ultra running introduces variables like elevation, terrain, sleep deprivation, and nutrition strategy that shorter races do not have. The 50K prediction shown here should be treated as a rough estimate. For distances beyond 50K, specialized ultra prediction models that account for elevation and aid station stops are more appropriate.
How can I improve my predicted times?
The fastest way to improve race predictions is to actually train for your target distance. Include a mix of easy runs, tempo runs, intervals, and long runs in your training. Consistency matters more than intensity. Most recreational runners see significant improvements in their first 1 to 2 years of structured training, with 5K times dropping by several minutes and marathon potential improving dramatically.
How do I predict my marathon time from a half marathon?
The simplest method is to double your half marathon time and add 10 to 20 minutes. A 1:45 half typically becomes a 3:40 to 3:50 marathon. The Riegel formula gives a more precise prediction: marathon time = half time x (42.195/21.0975)^1.06. Predictions from the half are the most reliable because the distance and physiological demands are closest to the full marathon.
How do I predict my marathon time from a 10K?
Multiply your 10K time by approximately 4.66 to estimate your marathon time. So a 50:00 10K predicts roughly a 3:53 marathon. The Riegel formula gives a more accurate prediction. Be aware that 10K predictions assume you have done the long-run training needed for the marathon distance. Without weekly long runs, your actual marathon will likely be slower than predicted.
What is a marathon prediction chart?
A marathon prediction chart is a reference table showing predicted marathon times based on common 5K, 10K, and half marathon results. The chart on this page covers 5K times from 18:00 to 35:00. Use it as a quick lookup, then use the calculator above for your exact result and three formula predictions.
Why does my marathon time predictor show a slower marathon than I expected?
The Riegel and Cameron formulas account for the natural slowdown over longer distances. If your training has been short and fast (lots of 5K work, no long runs), the predictor still applies the standard slowdown factor, which may match reality. If you have been doing 18 to 22 mile long runs, your actual marathon time may beat the prediction by a few minutes.
How It Works
Enter a recent race time
Pick a distance you have raced recently and enter your finish time. The more recent and accurate, the better your predictions will be.
Three formulas crunch the numbers
The Riegel, adjusted Riegel, and Cameron formulas each calculate your predicted finish time using different mathematical models of running fatigue.
Get predictions for every distance
See your predicted finish times for 1 mile through 50K, with pace per kilometer and per mile. The range between formulas gives you a realistic target window.
Tips for Accurate Predictions
Use a recent race for best accuracy
A race from the last 3 months gives the most reliable predictions. Old PRs may not reflect your current fitness. If you have not raced recently, do a timed effort at a local parkrun or track.
Predict up, not just down
Most runners use this to predict marathon times from shorter races. But it works both ways. If you have a marathon result, you can see what your 5K potential is and train specifically for that distance.
Train for the distance you want to race
Predictions assume you are properly trained for the target distance. A runner with a fast 5K but no long runs will likely run slower than their predicted marathon time. The formulas work best when your training matches your goal.
Use the range as your target window
The three formulas give slightly different results. Use the fastest as your A goal, the average as your B goal, and the slowest as your safe starting pace. This helps you race smart without going out too fast.
Marathon Prediction Chart
This chart predicts marathon finish times from common 5K, 10K, and half marathon results using the Riegel formula. Use it as a rough guide. The calculator above gives you the exact prediction with three formulas, plus pace per km and per mile.
Predictions assume comparable training across distances. A runner with strong 5K speed but no long runs will likely run slower than the predicted marathon time.
How to Predict Half Marathon Time from a 5K or 10K
The Riegel formula works just as well for half marathon prediction. Plug your 5K or 10K result into the calculator above and the half marathon prediction appears alongside the full marathon. As a quick mental shortcut, double your 10K time and add 7 to 9 minutes for a rough half marathon estimate. A 50-minute 10K usually translates to about a 1:50 half.
Predicting downward (long to short) also works. If you have a recent half marathon, the calculator will tell you what 5K and 10K times you should be capable of. This is useful for setting goals at shorter races and noticing if your 5K speed has fallen behind your endurance.
Why Race Predictions Are Sometimes Wrong
Mileage gap
A predictor cannot tell whether you ran 20 mile long runs in training. A runner with a strong 10K but only 30 weekly miles will almost always run slower than predicted at the marathon distance because the body has not adapted to the demand.
Race day conditions
Heat, humidity, hills, and wind can add 5 to 30 seconds per mile to your pace. The prediction assumes ideal conditions on a flat certified course. Adjust your goal pace down for hot or hilly races.
Race specificity
A pure speed athlete will outperform predictions at the 5K and underperform at the marathon. A pure ultra runner is the opposite. The Riegel formula works best when your training matches the target distance.
Old race data
A 5K from two years ago is not a useful input. Fitness changes month to month. Use a race result from the last 8 to 12 weeks for the most accurate prediction. If you have not raced recently, use a parkrun or a track time trial.
The Most Accurate Race Predictor: Tanda vs Riegel vs Cameron
Three formulas dominate race prediction. Riegel (1977) uses T2 = T1 × (D2 / D1) ^ 1.06. Cameron adjusts the exponent based on race distance, which makes it more accurate for marathons. Tanda uses weekly mileage plus average pace, which is why the Tanda race predictor is often cited as the most accurate race predictor for the marathon specifically. Our calculator runs Riegel and Cameron side by side so you see the range.
For a pure marathon race time predictor, the Cameron output is usually the safer goal. For a half marathon predictor or 10K prediction, Riegel is the gold standard. For first-time marathoners, take the predicted marathon time and add 2 to 3 percent to account for the back half slow down.
Half Marathon to Marathon Time and Other Conversions
Marathon time calculator from half marathon
Multiply your half marathon time by 2.11. A 1:45 half predicts a 3:41:45 marathon under good training. Use the calculator above for the adjusted Riegel and Cameron values.
Predict half marathon time from 5K
A 25:00 5K predicts roughly a 1:55 half marathon. The prediction assumes you have done at least four long runs of 10+ miles in the last 8 weeks.
Estimate marathon time from 10K
Multiply your 10K by 4.67. A 50:00 10K predicts a 3:53 marathon. Subtract 5 to 10 minutes if your weekly mileage is above 50.
Half marathon time to pace
Divide your half marathon time by 13.11 to get pace per mile, or by 21.0975 for pace per kilometer. A 2:00 half = 9:09 per mile or 5:41 per km.
