Race Time Predictor
Use your recent race performance to predict finish times at other distances. Enter your reference race result, and this calculator will estimate your potential at 5K, 10K, half marathon, marathon, and 50K based on proven race prediction formulas adjusted for training status.
Pace Units
Reference Race
Your Finish Time
Training Status
Your training status affects predictions for different distances. Well-trained = completed appropriate training volume for target distance.
ℹ️ About These Predictions
These predictions use the Riegel formula with adjustments for training status and distance ratios. The formula accounts for the fact that pace slows as distance increases due to fatigue accumulation and the shift from anaerobic to aerobic energy systems.
Confidence ranges: Predictions include uncertainty ranges (±3-7%) that widen for larger distance jumps. A 5K to marathon prediction has higher uncertainty than a 10K to half marathon prediction.
Predictions are most accurate when: 1) Reference race was within 6-8 weeks and represents current fitness, 2) You were well-trained and tapered for that race, 3) Race conditions were good, 4) Target distance is within 2-4x of reference distance, 5) You'll complete appropriate training for the target distance.
How to Use These Predictions
Use predicted times as goal targets, but consider the confidence range. If undertrained for your target distance, expect times closer to the upper bound. Well-trained athletes typically hit predictions within the confidence range.
Training status guide: Under-trained = inadequate mileage or long runs for distance; Well-trained = completed structured training plan with appropriate volume; Over-trained = excessive fatigue, declining performance, poor recovery.
Important note: Predictions assume similar course difficulty and weather. Adjust expectations for hilly courses, heat, altitude, or wind. For races with significant elevation, use the Race Planning calculator's elevation adjustment feature.
Frequently Asked Questions
Found an error or have suggestions? Please email me at stefan@bflcoaching.com