Race Time Predictor
Free race time predictor using the Riegel formula. Turn a recent 5K, 10K or half marathon result into predicted finish times, equivalent paces per km and mile, negative-split and fade scenarios, and easy, tempo and interval training zones. Runs in your browser.
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What is Race Time Predictor?
The Race Time Predictor takes one recent result and applies the Riegel exponent model to forecast your finish time at any other distance from the mile to the marathon. It shows pace per km and per mile for the target, bends the exponent to 1.04, 1.06 and 1.08 to contrast patient negative-split pacing against a late fade, and derives easy, long-run, tempo and interval training paces from the same numbers.
Key Benefits
- Realistic targets for every distance from a single recent race
- Pace per km and per mile, not just a finish time
- Negative-split, standard and fade scenarios on one table
- Training zones that follow your own current fitness
- Accepts h:mm:ss, m:ss or plain seconds and works entirely offline
Common Use Cases
- •Setting a half marathon goal off a recent 10K
- •Planning marathon pacing after a strong half marathon
- •Choosing between aggressive and conservative race plans
- •Refreshing easy, tempo and interval paces after a breakthrough race
- •Comparing what a 45:00 10K means for a friend racing a different distance
How to Predict Your Race Time
- Pick your recent race: Choose the distance you raced and type the finish time as h:mm:ss, m:ss or plain seconds. The more recent and the more evenly paced, the better the predictions.
- Choose the target distance: Select the race you are training for. The Riegel model with exponent 1.06 converts your result into a realistic finish time and pace per km and per mile.
- Check the pacing scenarios: The scenario table shows what patient negative-split pacing at 1.04 or a late fade at 1.08 does to the same target, so you can pick a race plan.
- Use the training zones: Take the easy, long-run, tempo and interval paces into your weekly training. They are derived from your own result, so they update automatically every time you race.
Key Features
- Riegel exponent predictions from 1 mile to the marathon
- Pace per km and per mile with average speed for every target distance
- Negative-split, standard and fade scenarios at exponents 1.04, 1.06 and 1.08
- Training zones for easy, long run, tempo and interval days
- Flexible time input accepting h:mm:ss, m:ss or plain seconds
- Copyable prediction summary, pure client-side math