Enter one recent race and the race predictor shows what you can run at every other distance, assuming you have trained for it.
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Your watch makes its own guess from its VO2 max estimate. See how far out the Garmin Race Predictor can be, and why mine was still wrong after a parkrun almost a minute faster than it predicted. Stryd users can also plan race-day power with the Stryd Race Calculator.
What to do with this number
- Check the pace for each prediction with the pace calculator or a chart: marathon pace chart, half marathon pace chart.
- Turn the same result into training paces with the VDOT calculator.
- Rank your times at your age: age grade calculator.
- Compare with your watch’s guess: Garmin Race Predictor.
- Choose a watch to track progress: best running watch.
- Build a 5K first with the 5k training plan.
Quick answers
How accurate is a race predictor?
Predictions are good between similar distances, such as 10K to half marathon, and least reliable from a 5K to a marathon, because the marathon depends on long runs and fuelling that a 5K does not test. A 20:00 5K predicts 41:42 for 10K, 1:32:00 for the half marathon and 3:11:49 for the marathon with Riegel’s formula, which is optimistic for the marathon.
What formula does the race predictor use?
It uses Pete Riegel’s formula, in which time rises with distance to the power of 1.06, and Jack Daniels’ VDOT tables. The prediction is the average of the two, and the range shows both.
How does the Garmin Race Predictor work?
Garmin makes its predictions from its own fitness estimates and training data rather than from one race, so they can differ from this calculator. Read Garmin Race Predictor and why it can be still wrong.
Can I predict a marathon from a 5K?
You can, but treat the number as a ceiling. If you have not done long runs, expect to finish slower than the number shown. The best predictor of a marathon is a recent half marathon or a long tempo run.
Which race result should I enter?
Use a hard, recent effort on a flat course in mild weather, ideally within the last six weeks. A time from a hilly or hot day will produce a slow prediction.
Why does my prediction differ from my watch?
Watches predict from heart rate and pace data, which move with fatigue and temperature. A race is a direct measurement, so use the race number when you have one.
Small things I always use
- Garmin 90-degree charging adapter: Charges your Garmin from any USB-C cable. Essential when travelling. I use one.
- Body Glide: The blue anti-chafe stick swimmers and runners carry. I use it.
- Speedo earplugs: Fewer ear infections and no cold-water dizziness. I use them.
- Dryrobe Advance: My winter changing robe for open-water swims. I use one. A cheaper option is the AONYIYI changing robe.
- Maurten: Race fuel that stays easy on the stomach. I use them.
- Beet It Sport nitrate shots: Beetroot shots I take in the days before a race. I use them.
- Garmin charging puck: The quickest way to top up before a session. I use one.
- Injinji: Toe socks that stop rubbing, so you run more. I use them.
- Ultimate toe protectors: Stop black toenails on long runs. They work. I use them.
- Compressport R2 v2 calf sleeves: My calf sleeves of choice. I use them.
- Cellucor C4: My pre-workout before hard sessions.
- TPU tubes: Schwalbe Aerothan, Tubolito and Pirelli SmarTube. Light, tiny spares. I use all three.
- G8 insoles: Adjustable insoles that are good. I use them.
- Cycplus Cube: A 97g electric pump that gets a road tyre rideable in two minutes. I carry one. 5% off with code THE5KRUNNER.
Watches and sensors
- Polar H10: My daily driver for waking HRV.
- Polar Verity Sense: My backup arm-worn HR sensor.
- Nomad bedside charger: Charges my iPhone and Apple Watch overnight. I use it, and many of their bands.
- Train.Red: The best muscle oxygen sensor I’ve used.
- Tymewear: Accurate heart rate and reliable ventilatory zones. I use it to pace endurance rides over an hour.
- Garmin Forerunner 970: A pro-grade triathlon watch. I use this.
- Apple Watch Ultra 4: My daily smartwatch. No phone needed on rides.
- Garmin Fenix 9 Pro: I’ve just bought one.
On the bike
- Continental GP5000 for everyday riding, and Aero 111 on the front for special occasions.
- Helmets: Specialized S-Works Evade 3 for road riding, and Rudy Project Wing for TT-style races. I use both.
- Ravemen FR300: A front light that mounts under your Garmin or Wahoo. I use one.
- Ravemen FR1000: The light and the computer mount in one unit, so nothing else goes on the bars. Better than mine.
- Ravemen FR1500SE: 1,500 lumens hanging under your Garmin, for proper night rides.
- Ravemen FR500: A brighter FR300 with the same mount.
- Wahoo TRACKR Radar: I use it on one bike and Varia on the other. They perform the same.
- Garmin Varia RTL515: Radar that warns you of cars from behind. I use this model.
- Wahoo ELEMNT Roam 3: The bike computer that’s easy to use. I use mine on most rides.
- Favero Assioma Pro RS2: Accurate power pedals that swap easily between bikes. I use this model.
Home and indoor training
- NPE Runn: Makes my basic treadmill smart, sending more accurate speed and distance to my watch and Zwift. I use it.
- Google Wifi: Keeps Zwift connected in my pain cave. I use it.
- Apple TV 4K: Zwift on the big screen. I use two.
- Google Nest Doorbell (wired, 2nd gen): My video doorbell, running in both Google Home and Apple Home. I use it.
Health, recovery and sleep
- FreeStyle Libre 3 Plus: Shows how my blood sugar responds to diet.
- hDrop: Measures my sweat loss in summer and indoors.
- Fourth Frontier Zone: Checks my heart under load in hard sessions.
- Kineon MOVE+: Red and infrared light for sore knees, Achilles and other joints after hard training. I use it.
- Oura Ring 5: My partner’s recovery tracker of choice.
- Eight Sleep: A cooling mattress cover my partner and I use nightly.
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