Heart rate
Heart-Rate Drift Calculator
Use this after a steady easy run. Enter first-half and second-half pace plus average heart rate to see whether the internal cost rose.
- Compares efficiency between two halves of a steady run.
- Works best on flat, even-effort easy runs.
- Large drift can reflect heat, fatigue, dehydration, or aerobic base still developing.
Heart-rate drift shows whether the same running output became more expensive later in the run.
- Use a steady easy run, not intervals.
- Enter average pace and heart rate for each half.
- Avoid runs with long stops, big hills, or major wind changes.
Around 0-5% is usually a controlled result. Higher values can point to heat, dehydration, fatigue, or aerobic fitness that still needs more easy volume.
- Repeat the test in similar weather.
- Slow down or shorten the run when drift is high.
- Use a chest strap if the watch trace looks erratic.
Use the result as a recovery and aerobic-base clue, not as a race prediction.
Heart-rate driftAerobic decouplingEasy runSensor accuracy
Related reading What Is Heart-Rate Drift? Learn why heart rate rises during a steady run and what beginners should do about it. Can You Trust Your Running Heart Rate? Understand wrist sensor errors, cadence lock, chest straps, and when heart-rate data is good enough. A Simple Heart-Rate Training Plan for Runners Use reliable data, easy aerobic running, 80/20 distribution, quality workouts, and drift checks.
Heart-rate calculators Heart-Rate Zone Calculator Estimate easy, steady, and hard running zones. Zone 2 Calculator Focus on the easy aerobic range beginners ask about most. Heart-Rate Drift Calculator Estimate aerobic decoupling from a steady run. Max Heart Rate Calculator Compare age estimates with observed hard-effort readings. Heart Rate Reserve Calculator Use resting and max heart rate for personalized ranges.
Did my heart rate drift too much?
Aerobic decoupling 5.4%
Moderate drift
Use this only for steady runs with similar terrain and effort.