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When and how to measure

It is very important that you measure your temperature using a basal thermometer with 2 decimals. You are not to use a regular fever thermometer together with Natural Cycles.

For those of you that just started, it's good to know that it will take a few weeks of measuring for Natural Cycles' algorithm to learn your unique cycle. The more data, the better can we know where in your cycle you are, so keep measuring! We recommend that you measure 5 times per week, so you can mark the temperature as deviating due to 'more/less sleep' on the weekends if you enjoy sleep-ins during those days.

Measure first thing when you wake up in the morning before you sit up or get out of bed.
The basal body temperature is our resting temperature, and it is lowest when we sleep. Moving too much will affect your body temperature and the result will be incorrect. We advise all Cyclers to measure at roughly the same time every morning after the same amount of sleep, within a ± 2h window of your usual morning alarm. If you decide to have a lie-in then we recommend that you still measure to keep up the habit and mark the temperature as deviating.

Place the thermometer under your tongue before you press ON.
Almost the entire purple part of the thermometer will be inside of the mouth when the thermometer is placed correctly. Close your mouth and breathe through your nose. Start measuring once the thermometer is correctly placed in your mouth. Wait for the beeps which indicate that the thermometer is done with measuring.

For the first 3 cycles, measure as often as possible to help the app get to know you.
The more data points you have, the better Natural Cycles can get to know you and know when you ovulate. The better Natural Cycles knows your cycles the more certain the algorithm is of when you ovulate, and in return, you will get a narrow window of fertile days.

Click here for more information on when to mark your temperature as deviating so that the algorithm doesn't take it into account in the calculations.


Remember that your temperature is what the algorithm is using to be able to confirm ovulation in each cycle. So if you have a lot of red, fertile, days it may be a good idea to check your graph if you haven't already. Please read more about how the app detects ovulation

Here is a video on how and when to measure your basal body temperature: