Apple Watch provides heart rate measurements that are generally accurate for resting and moderate exercise conditions, though accuracy declines during high-intensity or wrist-movement-heavy activities.

In plain English

The Apple Watch reads your heart rate within about 2 to 5 beats at rest and during steady running. It gets less reliable during fast intervals and anything with a lot of wrist motion.

Why it works

Photoplethysmography (PPG) sensors detect blood volume changes in the wrist's microvasculature. Green LEDs work best for continuous HR during exercise; infrared sensors are used for resting measurements. Motion artifacts from wrist movement can corrupt the PPG signal.

The evidence

• Lambe, R., Baldwin, M., O'Grady, B. et al. (2026). The Accuracy of Apple Watch Measurements: A Living Systematic Review and Meta-Analysis. npj Digital Medicine.

• O'Grady, B., Lambe, R., Baldwin, M. et al. (2024). The Validity of Apple Watch Series 9 and Ultra 2 for Serial Measurements of Heart Rate Variability and Resting Heart Rate. Sensors.

• Falter, M., Budts, W., Goetschalckx, K. et al. (2019). Accuracy of Apple Watch Measurements for Heart Rate and Energy Expenditure in Patients with Cardiovascular Disease: Cross-Sectional Study. JMIR mHealth and uHealth.

Why we call confidence high

A 2026 living systematic review and meta-analysis (Lambe et al.) confirms Apple Watch HR accuracy across multiple generations. Series 9/Ultra 2 validation (O'Grady et al. 2024) shows strong agreement with reference devices for RHR and HRV.

Where it applies

Healthy adults