Wrist Temperature
Definition
Nightly wrist temperature deviation from your personal baseline, as measured by Apple Watch Series 8 and later during sleep.
Important: This is NOT a fever thermometer. It shows deviations from YOUR baseline, not absolute temperature.
Why It Matters
Wrist temperature patterns can: - Support cycle tracking - Retrospective ovulation estimation - Improve period predictions - When used with Cycle Tracking - Indicate wellness changes - Deviations may accompany illness - Require no user effort - Automatically collected during sleep
How It's Measured
Apple Watch measures wrist temperature through: - Sensors in the back crystal - Sampling during sleep - Comparison to personal baseline established over time - Requires 5+ nights to establish baseline
Display: Shown as deviation from baseline (e.g., +0.3°C, -0.2°C)
Typical Patterns
| Pattern | Interpretation |
|---|---|
| Steady baseline | Normal variation |
| Elevated phase (menstruating individuals) | Likely post-ovulation (luteal phase) |
| Return to baseline | Likely pre-ovulation (follicular phase) |
| Unexpected elevation | May indicate illness, poor sleep, alcohol |
Confounders & Limitations
- Not absolute temperature - Can't detect fever directly
- Baseline needed - Takes days to establish
- Sleep required - Only measures during sleep
- Watch fit - Affects accuracy
- Environment - Room temperature, blankets matter
- Alcohol - Elevates wrist temperature
- Illness - May show elevated readings
Use Cases
- Cycle tracking - Retrospective ovulation confirmation
- Fertility awareness - Automatic temperature data
- Wellness signals - Noticing deviations
- Research/personal interest - Body temperature patterns
Integration with Cycle Tracking
When enabled: - Wrist temperature data enhances period predictions - Provides retrospective ovulation estimates - Requires consistent wear during sleep - Takes 2+ cycles to improve predictions
Important Notes
- This feature cannot detect pregnancy
- Not intended as a contraceptive tool
- Not a replacement for medical thermometers
- Individual patterns vary