Wrist temperature: definition and meaning
Wrist temperature is the skin temperature at your wrist measured overnight by a wearable, such as Apple Watch, and reported as a change from your personal baseline. Like basal body temperature, it tends to rise slightly after ovulation and fall before or around your period, so it can help estimate ovulation in hindsight. It is not a diagnostic measurement.
How wrist temperature tracking works
While you sleep, sensors sample your skin temperature many times. The watch builds a baseline over several nights and then shows each night as a small plus or minus against it. Apple Watch Series 8 and later and Ultra models record it with Sleep Focus on. A post-ovulation shift of a few tenths of a degree is what cycle features look for.
Wrist temperature vs basal body temperature
| Wrist temperature | Basal body temperature | |
|---|---|---|
| How | automatic, overnight, from a wearable | thermometer, same time every morning before getting up |
| Effort | low | high, needs daily habit |
| Measures | skin temperature change from baseline | core resting temperature |
| Affected by | room temperature, bedding, alcohol, illness, a loose strap | late nights, alcohol, illness, timing |
Both only show ovulation after it has happened. Read more about basal body temperature, Apple Watch wrist temperature and Apple Watch and ovulation.
Lulu can import your Apple Watch wrist temperature from Apple Health and show it beside your cycle and mood, so you can see the shift after ovulation. It is a helpful hint for your predictions, not a diagnosis and not contraception.
What else can move the line
Fever, a warm bedroom, alcohol, travel across time zones and poor sleep can all push wrist temperature up. In perimenopause, night sweats can add noise. Look for a pattern across several cycles rather than reading one night.
Frequently asked questions
Can wrist temperature confirm ovulation?
It can suggest ovulation happened when a sustained rise appears, but it does not confirm it the way a blood test or ultrasound does.
Does wrist temperature predict my period?
A drop in temperature often comes shortly before a period, which can support a prediction, but timing varies between people.
Sources
- Apple Support: Track your cycle with Apple Watch (wrist temperature)
- Zhu TY et al. Accuracy of wrist skin temperature for estimating ovulation. J Med Internet Res (2021)
This page is for information only and isn’t medical advice. If something worries you, please talk to a doctor.
Keep reading
How does Apple Watch wrist temperature work for cycles?Apple Watch wrist temperature tracks nightly changes from your baseline. How it relates to your cycle, how to read the chart, and what affects it.Basal body temperature (BBT): definition and meaningBasal body temperature (BBT) is your lowest resting temperature. How it rises after ovulation, how to read a BBT chart, and what it can't tell you.Can Apple Watch track ovulation?Apple Watch ovulation estimates use wrist temperature on Series 8 and later. How it works, what you need, why it's retrospective, and how to use it well.Apple Watch period trackers: what works with your watchWhich Apple Watch period tracker fits you? Apple Cycle Tracking, Natural Cycles, Clue, Flo, Stardust and Lulu compared on wrist temperature and watch use.
Ovulation: definition and meaningOvulation is when an ovary releases an egg, usually 12 to 14 days before your next period. Signs, timing, the fertile window, and how it affects mood.