How iOS 15 Health Trends Alerts Work

With the release of iOS 15, Apple introduced an intelligent trend analysis system in the Health app designed to help users track long-term patterns in their well-being. This feature continuously evaluates metrics like heart rate, activity, sleep, and mobility, automatically alerting users when a significant upward or downward shift occurs. The following breakdown explains how the algorithm detects these patterns, how notifications are delivered, and how to manage them.

Data Collection and Baseline Calculation

The Health app analyzes more than 20 types of health and fitness metrics collected by an iPhone, Apple Watch, or compatible third-party accessories. Rather than reacting to daily fluctuations, the system calculates a historical baseline for each metric over weeks or months. Metrics tracked for trends include:

  • Resting heart rate and walking heart rate average
  • Daily steps, distance, and active energy
  • Sleep duration
  • Cardio fitness (VO2 max)
  • Walking steadiness and walking asymmetry

Trend Detection Algorithm

The trend analysis engine uses an internal algorithm to compare recent averages against historical baselines. When a metric consistently deviates from its normal range—either positively or negatively—the system registers a new trend. Because the system prioritizes sustained changes, it filters out temporary outliers, such as a single day of high activity or a temporary lack of sleep due to travel.

Delivery of Trend Alerts

When a meaningful shift is identified, the Health app alerts the user through a push notification.

  1. Notification Banner: A notification appears on the Lock Screen or Notification Center stating that a new trend has been spotted (for example, a sustained increase in resting heart rate or a decrease in daily step count).
  2. Detailed Overview: Tapping the notification takes the user directly to the Trends section within the Health app.
  3. Visual Context: Inside the app, the trend is displayed as an interactive chart showing the exact timeframe of the shift, the percentage or numerical change compared to the baseline, and contextual educational information explaining why that metric is important to overall health.

Managing Trend Notifications

Users have direct control over whether they receive these proactive updates. To adjust trend alerts:

  1. Open the Health app on iOS 15.
  2. Tap your Profile picture or icon in the top-right corner.
  3. Select Notifications.
  4. Toggle Trends on or off to enable or disable future alerts.