Zone2CalStart with a recent result.
A recent 5K, 10K, half marathon, or marathon gives the model a current fitness anchor before it predicts another distance.
Race Time Predictor
Turn one recent result into goal pace, splits, and race-day targets.
Project 5K, 10K, half, and marathon times, then adjust for weather, fueling, and training pace in one view.
🏁 Race prediction & goal pace
Predict a target race or lock in a manual goal time to see required pace, splits, and fueling guidance instantly.
Recent result
Target race
Marathon presets:
Half-marathon presets:
Predicted/goal finish
—
Required average pace
— min/km
Saved calculations stay in this browser so repeat visits can reopen the same goal quickly.
Split chart
Advanced conditions, fueling & training tools
Tip
Use 1.03–1.04 for aggressive pacing, 1.06 default, and 1.07–1.08 for conservative endurance-focused attempts.
Weather adjustment
Adjusted time: —
Fuel & hydration
Total carbohydrate: — g (≈ — gels)
Total sodium: — mg, fluids: — ml
Estimated calories: — kcal
Training pace guide
- • Easy: — /km (— /mile)
- • Marathon pace: — /km (— /mile)
- • Tempo (half): — /km (— /mile)
- • Threshold (10K): — /km (— /mile)
- • Intervals (5K): — /km (— /mile)
Weekly 80/20 planner
Easy (80%): — km, Quality
(20%): — km
Interval session planner
Rep pace
— /km
Rep time: —, Rest: —
How should you use a race time predictor?
Adjust for the actual race day.
Heat, humidity, wind, altitude, hills, and fueling can shift the final target, so use the adjustment fields before committing to a pace band.
Validate with heart rate and long runs.
If predicted pace drifts above your LT or creates heavy heart-rate drift late in long runs, choose the conservative target.
Frequently Asked Questions
These answers match the structured FAQ data on this page.
How accurate is the race time predictor?
It provides a strong baseline from your recent result using the Riegel model. Accuracy improves when your target race and training conditions are similar.
Can I predict marathon pace from a 10K result?
Yes. The tool extrapolates across distances and then lets you adjust for weather, altitude, and pacing strategy.
Should I still run by heart rate?
Yes. Use predicted pace as a target and cross-check with heart-rate zones, especially in heat, wind, and long races.
Last updated: February 25, 2026