Enter a recent race result — the distance and your finish time (hours, minutes, seconds) — and the Race Predictor Calculator projects your equivalent performances across popular distances from the 1 mile all the way up to the marathon. You also get predicted training paces for easy runs, tempo efforts, and intervals based on your current fitness.
Predicted Marathon Time
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1 Mile
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5K
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10K
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Half Marathon
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Easy Run Pace
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Tempo Pace
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Interval Pace
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This calculator uses a fatigue factor model based on the Riegel formula: T2 = T1 × (D2/D1)^1.06. The exponent (1.06) accounts for the physiological fact that performance degrades at longer distances — you can't simply scale pace linearly. It's one of the most widely validated models in running science.
Predictions are most accurate when your input race was recent (within the last 8–12 weeks) and run at full effort under normal conditions. Predictions can vary based on course terrain, weather, training status, and individual physiology. Use them as a guideline rather than a guarantee.
Yes — enter your recent race result and compare the predicted marathon time against the Boston Athletic Association's qualifying standards for your age and gender. Keep in mind that BQ standards are based on chip time and course conditions vary, so treat the prediction as an estimate.
Predictions are most reliable when the input and target distances are relatively close. For example, a recent 10K gives a very good half marathon estimate. Predicting a marathon from a 5K introduces more uncertainty since the physiological demands differ significantly over longer distances.
Training paces (easy, tempo, interval) are derived from your equivalent race velocity using established percentage-of-effort guidelines. Easy runs are typically 55–75% of race effort, tempo runs around 83–88%, and intervals at 95–100% of 5K effort. These ranges help you train at the right intensity.
Choose whichever unit matches how your GPS watch or training plan displays pace. The calculator supports both — select 'Miles (min/mi)' or 'Kilometers (min/km)' using the Pace Units toggle. Both options use the same underlying distance calculations.
Ideally your race should be within the last 8–12 weeks and reflect your current fitness level. An old PR from years ago will overestimate your current capability. If you've been injured or undertrained, your predictions may also run optimistic — always pair predictions with honest self-assessment.
The Riegel formula used here is gender-neutral — it predicts based solely on the relationship between effort and distance. Some advanced models apply different fatigue exponents for men and women. If you want gender-specific predictions, tools like the VDOT calculator (Jack Daniels) offer an alternative approach.