Race time predictor.
Enter your recent race result and we’ll predict finish times for other distances using the Riegel model. Switch between metric and imperial, and see a full table of predictions.
Predict times from a recent result
Enter hours, minutes, seconds separately (e.g., 0 • 50 • 0 for 50 minutes).
Predicted times table
| Distance | Predicted Time |
|---|---|
| 1 km | — |
| 1 mile | — |
| 5 km | — |
| 10 km | — |
| Half marathon | — |
| Marathon | — |
Interpreting your prediction
Enter a recent result and target distance to see a personalised explanation here, including equivalent pace per km/mi, an overview of likely pacing adjustments, and environmental factors to consider.
Use the dynamic summary to answer three questions: Can I realistically hold the predicted pace? What fueling or pacing tweaks will help? and How does this align with my current training load? If the prediction feels aggressive, extend your build with threshold work and long-run progressions before re-testing.
Training adjustments by predicted goal
Once you see your target pace, align your weekly structure with the physiological demands of the race you’re planning. The table below outlines sample focuses for common predictions.
| Predicted event | Key sessions | Fueling focus | Strength & mobility |
|---|---|---|---|
| Fast 5K (sub-22) | Track intervals (400–1,000 m), hill sprints, strides twice weekly | Simple carbs 30 minutes before hard sessions | Hip/ankle plyometrics, drills for turnover |
| Breakthrough 10K (sub-46) | Tempo intervals (3 × 10 min), long run with last 20% at goal pace | Practice fueling if race lasts >45 minutes; hydrate according to sweat rate | Core stability, single-leg strength |
| Half marathon PB (sub-1:40) | Progressive long runs, cruise intervals, midweek medium-long run | Dial in gels every 30–35 minutes; rehearse breakfast timing | Glute medius work, calf raises, mobility for hips |
| Marathon sub-3:30 | Long runs with goal-pace blocks, tempo + marathon combo workouts | Full fueling plan (60–90 g carbs/hr) and hydration test runs | Posterior chain strength, stability circuits twice weekly |
Adjust the plan if your predicted pace differs from the workouts you currently complete. When the calculator suggests a big leap, build an intermediate goal race to bridge the gap.
Example use cases
Coaches and self-coached runners use the predictor in diverse scenarios:
- Race-distance transitions: move from a sharp 5K to a first half marathon by checking how much slower the predicted pace is and planning aerobic volume accordingly.
- Season planning: map out A/B/C races with predicted times to ensure taper lengths and training blocks support realistic goals.
- Team seeding: assign workout groups by predicted marathon pace so long-run packs stay cohesive.
- Fuel strategy testing: simulate predicted marathon pace during long runs to practice gel intervals and check stomach tolerance.
Log each prediction with notes on weather, surface, and fatigue. When the real race arrives, compare the actual result to refine your exponent and pacing strategy for next time.
Adapting predictions for conditions
Once you have a baseline finish time, adjust for course and climate:
- Heat: reduce predicted pace by 5–10 seconds per kilometre when temperatures exceed 20 °C (68 °F), or follow a heat-adjusted pace chart.
- Elevation gain: add 10–15 seconds per 100 m of climbing for road races, more for technical trails.
- Altitude: subtract 3–5% from predicted finish time above 1,500 m unless you live and train at altitude.
- Surface: trail, sand, or snow may slow pace by 15–25% depending on technicality; compare with similar course data when possible.
Create contingency plans (A/B/C goals) so you can pivot on race day if weather shifts or splits trend slower than predicted.
Race predictor FAQs
Open the accordions to learn how the model behaves in different situations.
How does the Riegel exponent affect predictions?
A lower exponent (≈1.03) assumes you hold pace better as distance increases, producing faster long-distance predictions. A higher exponent (≈1.08) anticipates more slowdown. Compare with your race history to find the sweet spot.
Can I use a training time instead of a race?
Yes, but adjust for conditions. Training runs without taper or race-day adrenaline often underperform by 1–3%. Add that buffer before predicting other distances.
What if my predicted pace feels unsustainably fast?
Use the pace calculator to break the prediction into lap splits, then test the pace in controlled workouts. If form breaks down quickly, choose a more conservative goal or extend your training block.
How do I handle ultra-distance predictions?
Beyond the marathon, increase the exponent or switch to time-on-feet models. Long aid-station stops and terrain variability make straight power-law predictions optimistic.
When should I update my inputs?
After every significant race or time trial. Recent performances give the best snapshot of current fitness and keep predictions anchored in reality.
Inside the race-time formula
Predictions use the Riegel power-law model: T₂ = T₁ × (D₂ ÷ D₁)k. We convert every distance to metres (1 mile = 1609.34 m) and every time to total seconds so that the ratio works regardless of units.
How the calculation unfolds
- Interpret your recent result as D₁ and T₁, converting inputs to metres and seconds.
- Convert the target distance D₂ to metres, raise the distance ratio to the exponent k (default 1.06), and multiply by T₁ to get T₂.
- Derive equivalent pace per km/mi by dividing the predicted time by the target distance in the respective units.
Choosing an exponent
| Exponent k | Best suited for | Pluses | Minuses |
|---|---|---|---|
| 1.03–1.05 | Track/short-road specialists with strong speed endurance. | Produces ambitious marathon/half predictions when you hold form well beyond 10K. | Optimistic for athletes building endurance or racing in tough conditions. |
| 1.06 (default) | General road runners moving between 5K and marathon. | Matches large-sample race datasets; easy to compare with most online tools. | May slightly understate potential in short events for speed-focused runners. |
| 1.07–1.10 | Marathon-to-ultra efforts, hot/hilly courses, or limited aerobic base. | Adds extra fade for fatigue, fuelling, and terrain so goals stay realistic. | Conservative if you execute a dialled-in marathon build on a fast course. |
Alternative calculators (Cameron, Daniels VDOT, McMillan) tweak the exponent or incorporate proprietary adjustments, but they follow the same power-law pattern. Track your own race history, see whether predictions skew high or low, and adjust k accordingly.