Race Time Predictor
Predict your finish time at any race distance from a recent result. Uses the VDOT formula for more accurate predictions than the Riegel method.
How Race Time Prediction Works
This tool uses your recent race result to calculate your VDOT score, then uses that score to predict how fast you could race at a different distance. It accounts for the fact that the relative aerobic cost of running changes with distance — a 5K and a marathon demand different energy systems.
VDOT vs. the Riegel Formula
The classic Riegel formula uses a fixed fatigue exponent (1.06) that assumes a simple power relationship between distance and time. The VDOT method models the actual physiology: aerobic contribution changes with duration, and the %VO₂max you can sustain for 10 minutes differs from what you can hold for 3 hours.
For predictions within a similar distance range (5K to 10K, half to full marathon), both methods produce similar results. For large jumps in distance, VDOT is more accurate.
Limitations
Predictions assume equal fitness and similar conditions. Factors that affect accuracy:
- The source race must be a maximal effort — a conservative or poorly paced race underestimates your fitness
- Training specificity matters — marathon-trained runners often outperform their VDOT-predicted 5K and vice versa
- Course profiles, weather, and terrain are not accounted for