The iPhone 17 and the Apple Watch are both popular Apple devices used for tracking physical activity, but they differ significantly in their design, sensors, and accuracy of fitness data. Understanding how each device performs can help users choose the best tool for their health and fitness monitoring needs.
Step Tracking Accuracy
The iPhone 17 uses its built-in accelerometer and other sensors to count steps, which it records through the Health app. Since the iPhone is often carried in a pocket or hand, it can provide a relatively accurate step count over time. However, studies have shown that the iPhone tends to underestimate steps by about 12-21% compared to waist-worn pedometers or accelerometers, mainly because the phone is not always on the person during all activities. In controlled conditions, the underestimation is less pronounced but still present.
In contrast, the Apple Watch, worn on the wrist, continuously tracks steps and other movements more directly. According to a comprehensive meta-analysis of 56 studies by the University of Mississippi, the Apple Watch delivers highly accurate step counts with a mean absolute percent error of about 8.17%, which is well within the range considered excellent for consumer wearables[1][2][3]. The wrist placement and continuous wear make the Apple Watch more reliable for step tracking than the iPhone.
Heart Rate Monitoring
The Apple Watch excels in heart rate monitoring, offering data that is clinically acceptable and highly accurate for most users, including those with cardiovascular conditions, based on peer-reviewed studies. The University of Mississippi meta-analysis confirmed a mean absolute percent error of just 4.43% for heart rate measurements across various Apple Watch models[1][2][3].
The iPhone 17, however, does not have dedicated heart rate sensors like the Apple Watch. It cannot directly measure heart rate without external accessories or apps that use the camera or third-party devices. Therefore, for heart rate tracking, the Apple Watch is clearly superior.
Calorie Burn Estimation
Both devices attempt to estimate calories burned, but this metric remains a challenge for consumer devices. The Apple Watch’s calorie estimates have been found to be significantly less accurate, with an average error rate of nearly 28% across different activities such as walking, running, and cycling[1][2][3]. This means users should treat calorie data as a motivational guide rather than precise measurements.
The iPhone 17, relying on step counts and general movement data without the detailed physiological inputs available to the Apple Watch, is likely even less accurate in estimating calories burned. There is no direct study comparing the iPhone 17’s calorie tracking accuracy, but given the iPhone’s limitations, it is reasonable to infer it is inferior to the Apple Watch in this regard.
GPS and Distance Tracking
When it comes to GPS-based tracking for distance and route mapping, the Apple Watch generally provides more consistent and refined data due to its dedicated GPS chip and optimized algorithms. The iPhone’s GPS is accurate but can be affected by how and where the phone is carried. Users have reported discrepancies in distance and route tracking between the iPhone and Apple Watch, often due to differences in GPS hardware and software processing.
Summary
- Step Counting: Apple Watch is more accurate (~8.17% error) than iPhone 17 (underestimates by 12-21%).
- Heart Rate Monitoring: Apple Watch provides clinically validated, highly accurate heart rate data; iPhone 17 does not have built-in heart rate sensors.
- Calorie Estimation: Both devices have significant error margins, but Apple Watch is better studied; iPhone 17 likely less accurate.
- GPS & Distance: Apple Watch generally offers more reliable GPS tracking than iPhone 17.
Conclusion
The Apple Watch remains the more accurate and comprehensive device for tracking physical activity compared to the iPhone 17. Its dedicated sensors, continuous wear, and advanced algorithms allow it to deliver reliable heart rate and step count data, while the iPhone 17’s tracking is limited by its form factor and sensor capabilities. For users focused on detailed fitness tracking and health monitoring, the Apple Watch is the superior choice. The iPhone 17’s built-in tracking is useful for general activity monitoring but should be considered less precise, especially for metrics beyond step counting.
Users should view all wearable and phone-based fitness data as helpful guidance rather than exact medical measurements, particularly for calorie burn estimations where errors remain significant[1][2][3].
[1] https://appleinsider.com/articles/25/06/05/new-study-reveals-where-the-apple-watch-gets-fitness-data-right—-and-wrong
[2] https://www.phonearena.com/news/study-apple-watch-fitness-tracking-test_id171051
[3] https://www.macrumors.com/2025/06/05/apple-watch-gets-fitness-metric-wrong/