VO2 Max Estimator & Marathon / Half Marathon Race Predictor
Estimate your VO2 max and predict your full or half marathon finish time from a recent 5K or 10K result
Estimates your VO2 max from a recent 5K or 10K time and projects your expected finish time for a full or half marathon.
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🔒 Everything runs 100% in your browser. Your files and input are never uploaded to any server.
How to use
- Enter your recent race distance (5K or 10K) and finish time (minutes/seconds).
- See your estimated VO2 max and projected full/half marathon times.
FAQ
- What race-prediction formula does this use?
- It applies Riegel's fatigue-factor formula alongside Jack Daniels' VDOT formula, both well-established in sports science.
- Can my predicted time differ from my actual race result?
- Yes — this is a theoretical estimate based on your current fitness level. Actual results depend on pacing strategy, course difficulty, weather, and how you feel on race day, so treat it as a reference rather than a guarantee.
- Does entering both a 5K and 10K time improve accuracy?
- Yes, entering both lets the calculator average your fatigue factor across two data points, giving a more reliable prediction than a single race time alone.