Race Time
Predictor
Predict your finish time for any race distance based on a recent result. Powered by VO2max, the same formula used by coaches worldwide.
Your Race Result
Predicted Race Times
Assumes equal training for the target distance
How race time prediction works
Race time prediction uses the relationship between VO2max utilisation and race duration. When you race a shorter distance all-out, you're using a known percentage of your aerobic capacity. That percentage changes predictably as the distance increases.
Snel uses VO2max, from Jack Daniels' Running Formula. It takes your recent race result, estimates your VO2max (a proxy for running fitness), and maps it to equivalent performances at other distances.
For example, if you ran a 5K in 25:00, the predictor estimates roughly a 51:50 10K, a 1:55 half marathon, and a 4:01 marathon. These assume equal training for the target distance, which is an important caveat.
Understanding VO2max
VO2max is not VO2max, although they're related. VO2max accounts for running economy and VO2max together. Two runners can have the same VO2max but different VDOTs because one runs more efficiently.
Your VO2max number typically falls between 30 and 80. A beginner runner completing their first 5K might have a VO2max around 30-35. A competitive club runner sits around 50-55. Elite runners reach 70+.
The useful thing about VO2max is that it maps directly to training paces. Once you know your number, you know exactly how fast to run your easy runs, tempos, and intervals. Try the VO2max Calculator to see your full training zones.
When predictions are accurate (and when they're not)
Predictions work best when:
- Your input race was a genuine all-out effort
- The race was recent (within 4-6 weeks)
- You're equally trained for the target distance
- The race was on a flat course in fair weather
Predictions are less reliable when:
- You haven't trained for the longer distance
- Your race was hilly or on trail
- Weather was extreme (hot, windy, altitude)
- You paced the race badly
- Predicting a much longer distance (5K to marathon)
The biggest source of error is training specificity. A 5K runner's predicted marathon time assumes they've put in the long runs and marathon-specific training. Without that volume, the actual time will be slower than predicted.
Common prediction examples
| Input Race | 5K | 10K | Half | Marathon |
|---|---|---|---|---|
| 5K: 20:00 | 20:00 | 41:30 | 1:31:33 | 3:11:50 |
| 5K: 25:00 | 25:00 | 51:50 | 1:54:56 | 4:01:07 |
| 5K: 30:00 | 30:00 | 1:02:36 | 2:19:01 | 4:52:52 |
| 10K: 45:00 | 21:40 | 45:00 | 1:39:30 | 3:28:38 |
| 10K: 55:00 | 26:30 | 55:00 | 2:01:55 | 4:16:02 |
| Half: 1:45:00 | 22:58 | 47:42 | 1:45:00 | 3:40:06 |
| Half: 2:00:00 | 26:22 | 54:46 | 2:00:00 | 4:13:19 |
These are estimates based on VO2max equivalences. Your actual result depends on training, course, and conditions.
Using predictions for goal setting
A prediction gives you a realistic starting point. If the predictor says you're capable of a 1:50 half marathon based on your 10K time, that's a reasonable target with proper training.
Be honest about your training. If you've only been running 5K and want to predict a marathon time, the number on screen assumes marathon-specific preparation. Add 10-15 minutes to the predicted marathon time if you haven't done the long runs yet.
Snel uses VO2max to set your training zones automatically. When you log a race result, the app recalibrates your zones so every workout reflects your current fitness.
Frequently asked questions
How accurate are race time predictions?
For similar distances (5K to 10K), predictions are typically within 1-2 minutes. For larger jumps (5K to marathon), accuracy depends heavily on whether you've trained specifically for the longer distance.
Which race result should I use as input?
Your most recent all-out effort on a flat course. A parkrun PB from last month is better than a hilly 10K from six months ago.
Can I predict my time from a training run?
It's less reliable. Training runs rarely match race effort. If you must, use a recent tempo run or time trial, but expect the prediction to be slightly optimistic.
Why does my predicted marathon time seem too fast?
The prediction assumes you've done marathon-specific training. If you haven't built up to long runs of 30-35 km, your actual time will be slower. Use the prediction as a ceiling, not a guarantee.
What VO2max do I need for a sub-2 hour half marathon?
Approximately VO2max 43. That corresponds to roughly a 24:30 5K or 50:50 10K.
Does altitude affect the prediction?
Yes. Running at altitude reduces performance. Predictions assume sea-level conditions. If your input race was at altitude, your actual sea-level fitness is likely better than predicted.
Can I use a treadmill race result?
Treadmill paces tend to feel easier than outdoor equivalents due to lack of wind resistance and the belt assisting leg turnover. Use outdoor results for better accuracy.
Train for your predicted time
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