Understanding when your ovulation occurs is key to understanding when you’re fertile – and therefore understanding when you’re most (or least) likely to get pregnant.
How Natural Cycles predicts ovulation
Before being able to detect ovulation, the algorithm has to predict ovulation. As you’re most fertile before ovulation, predicting ovulation plays a key role in successfully preventing and planning a pregnancy.
Natural Cycles makes a prediction for the upcoming ovulation day based on your historical data, such as your average ovulation day, cycle length, etc. While this prediction is based on your past data, every cycle is unique; therefore, Natural Cycles will never assume that your ovulation occurs on the same day in each cycle.
For NC° Birth Control users, the algorithm will give a buffer of red days before the predicted ovulation. How large this buffer needs to be depends on several factors – mostly, how much data was logged in the past and how regular your cycle is.
As a new NC° Birth Control user, the algorithm doesn't have much information on when you usually ovulate and how that varies, so you’ll get a greater buffer of red days in the beginning of the cycle for the first few cycles. You can learn more about how long it takes for the algorithm to get to know you here.
For NC° Plan Pregnancy users, the buffer of red (fertile) days before ovulation is smaller, as it’s more important to better isolate the fertile window when using NC° for trying to get pregnant.
If you’re past the predicted ovulation day, you won’t see the ovulation symbol until the algorithm has confirmed ovulation. While the algorithm is waiting for more data to confirm ovulation, you will see a clock icon in your predicted ovulation window.
How Natural Cycles can determine if ovulation has happened
When ovulation has occurred, the body enters the luteal phase. In the luteal phase, which is a non-fertile part of your cycle, the body releases progesterone, a hormone that aids in the development of the fetus if conception occurs. Because of the higher levels of progesterone, the temperature increases in the luteal phase. This temperature increase can be seen in the graph in the app – on average, a rise of 0.3 °C or 0.5 °F.
When the temperature has risen enough and has stayed elevated for long enough, the algorithm will therefore be able to confirm that ovulation has occurred. It will then calculate the most likely ovulation day from the temperature curve.
How fast the algorithm confirms ovulation after increased temperatures depends on different factors, such as cycle regularity, LH test results, and how much data was logged for the current and previous cycles.
Only if and when ovulation has been confirmed by a clear enough temperature rise will the algorithm start giving green days again (for both NC° Birth Control and NC° Plan Pregnancy users).
How Natural Cycles can identify ovulation day
After the algorithm has confirmed that ovulation has happened, it will identify when ovulation most likely happened. To do this, the algorithm will look at the temperature curve for the entire cycle. It will not look at individual temperature values since a single data point can fluctuate for many reasons and should not be given as much importance. Many factors, weights, and parameters are used in this statistical analysis.
Testing your LH level when the app sends you LH recommendations will help the algorithm pinpoint the ovulation day. However, for NC° Birth Control users, please keep in mind that the algorithm will not confirm your ovulation unless your temperature data supports that ovulation has occurred.
In the picture above, we can see the temperature increase that occurs after ovulation. This increase in temperature is what the algorithm is searching for to confirm that ovulation has occurred (in this case, on CD17). Usually, the algorithm requires 2-4 higher values before ovulation can be confirmed. If you see the ovulation symbol disappear, keep measuring, and the algorithm will soon be able to place your ovulation.
Can the algorithm move my ovulation?
The algorithm may move the most likely ovulation day to another day should your newly added data support this.
For instance, your ovulation day may be adjusted once you log your next period.
The luteal phase is consistent in length (although the length varies from person to person), which means that your period will most likely start after the same number of days after ovulation in each cycle. As a result, the luteal phase gives more information about when ovulation happened. In cases where there isn’t good enough temperature data, the algorithm can both come to move the most likely ovulation day as well as narrow down the ovulation window (if there is one) when it gets more data from the luteal phase. This means that once you start your next cycle with a period entry, your ovulation day for the cycle that just ended may be adjusted accordingly.
To ensure that the algorithm doesn’t need to move your ovulation, it’s important to keep on measuring according to our guidelines and to log at least five temperature entries per week.
To understand if your red and green days can change in the past click here.
What happens if I don’t ovulate?
The algorithm is able to detect anovulatory cycles (cycles with no ovulation). Read more about this here.