Nightly skin temperature is what actually shifts across a cycle. The ring measures it while you sleep, so phases and dates come from this month rather than an average of the last three.
Luteal
Day 18 of 29Temperature is 0.3°C above your follicular average — which is what the prediction reads.
Nightly skin temperature, this cycle
The rise after ovulation is a few tenths of a degree — too small to feel, and easy to miss with a thermometer you sometimes remember. Worn every night, it is the most reliable marker a wearable has.
Days 1–5
Menstrual Temperature at its lowest. Resting heart rate often settles; energy scores can read low for a day or two.Days 6–13
Follicular The steadiest window for most people — sleep and HRV usually sit at their best here.Around day 14
Ovulation A small temperature rise that holds. This is the shift the prediction is built on.Days 15–29
Luteal Warmer nights, slightly higher resting rate, often lighter sleep towards the end.Cycle lengths vary, and so do you. The app labels phases from your own measurements rather than assuming a 28-day textbook month.
Logging only. The app records temperature, symptoms and dates, and says plainly that it does not have enough to predict from yet.
Predicted windows appear with a range attached — "period expected in 11 to 13 days" rather than a single confident day.
The range narrows as your pattern establishes, and widens again by itself if your cycle changes. Irregular months are shown, not smoothed away.
Circular is not a contraceptive, does not prevent pregnancy, and is not intended to diagnose any condition.
Cramps, headaches, mood, sleep, spotting — tag them in a tap and they appear alongside sleep, stress and recovery for the same day. Over a few months the app can tell you which symptoms track your phases and which do not.
Switch modes and the Circle changes shape: cycle predictions step aside for week-by-week guidance, and your vitals are read against pregnancy rather than against a cycle.
Weeks 1–13
Resting heart rate usually climbs early. Sleep gets interrupted before it gets short.
Weeks 14–27
Often the steadiest stretch. Useful for establishing what your new normal looks like.
Weeks 28–42
Sleep fragments and temperature runs warmer. The app expects both rather than flagging them.
Pregnancy mode is guidance built on your own measurements. It is not a substitute for antenatal care, and not intended to diagnose any condition.
No. Circular is not a contraceptive device and must not be used to prevent pregnancy.
Usually two to three. The app shows a widening or narrowing range so you can see how confident it is rather than guessing.
The temperature shift is measured each month, so an unusual cycle is read as it happens rather than predicted from an average. Ranges stay wider, which is the honest answer.
It can flatten the temperature pattern the prediction relies on. The app still tracks symptoms, sleep and recovery, and is explicit when it cannot see a shift.
It stays in your account and is never shared without your action. The Circle can also be hidden entirely if you would rather it were not on your home screen.
No. Cycle tracking, symptom logging and pregnancy mode are included with the ring, permanently.
Suivant
Wear it through a month and the pattern is yours, measured rather than assumed.
Wear it through a month and the pattern is yours, measured rather than assumed.
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