Free Tools
Running Calculators
Free, science-based tools for runners. No signup required. Enter your numbers and get instant results.
Race prediction
- Race Time PredictorEnter a recent race result and predict your finish time at any distance, from 5K to marathon. Powered by the Riegel formula.Calculate →
- Running Performance CalculatorAdjust your race time for altitude, course grade, heat, humidity, wind, and age to find your true sea-level equivalent performance.Calculate →
- Race Pacing & Fueling PlannerUpload your course GPX and a goal for an elevation-aware, even-effort pacing plan plus a carb, fluid, and sodium timeline mapped to the course.Plan my race →
Training zones & fitness
- Training Pace CalculatorGet your personalised training zones from a recent race result: easy, tempo, threshold, and more. Based on Jack Daniels' VDOT system.Calculate →
- Lactate Threshold & LTHR CalculatorEstimate your lactate threshold heart rate and threshold pace from a 30-minute time trial or 5K/10K race. Get five training zones anchored on your threshold.Calculate →
- VO₂ Max EstimatorEstimate your aerobic capacity from any race result. See how your fitness compares to other runners and where you sit on the athlete spectrum.Estimate →
- Heart Rate Zone CalculatorCalculate your five heart rate training zones using Max HR percentage, the Karvonen heart rate reserve method, or LTHR-based Friel zones.Calculate →
- Aerobic Decoupling CalculatorCalculate Pa:HR aerobic decoupling from your run's first and second halves. Under 5% signals a strong aerobic base; over 8% means the effort was above threshold.Calculate →