When ovulation occurs, one of the ovaries releases an egg (an oocyte). The egg then travels down the fallopian tubes and may be met by a sperm and become fertilized.
When does ovulation occur?
On average, ovulation occurs between 12 and 16 days before your period starts. Depending on your unique cycle, it could be a couple of days earlier or later.
The average ovulation day for our Cyclers is Cycle Day 18 (the 18th day since the start of the cycle). It’s important to keep in mind that ovulation doesn’t always happen on the exact same day each cycle; the ovulation day may vary from one cycle to the next.
You can learn more about your own ovulation patterns in your Cycle Insights page (accessible via the Today view > See cycle insights), where you can see your average ovulation day and variation, as well as your earliest and latest ovulation day.
How can you know when ovulation occurs in your cycle?
Directly after ovulation, the progesterone level in the body increases, which causes the body temperature to rise. Measuring the body temperature is therefore an indirect measurement of the progesterone levels in the body. For that reason, the temperature rise is the most important indicator to confirm that ovulation has occurred in the cycle. If the algorithm finds a sustained temperature rise, it confirms ovulation occurred in that cycle. Learn more about ovulation detection here.
Your body also releases luteinizing hormone (LH) to initiate ovulation. You can test for the LH surge with LH tests (also called ovulation tests), which can help better understand the timing of ovulation. You can read more about LH here.
Natural Cycles uses temperature data, period data, and optional LH data to calculate a daily fertility status. The fertile window is six days in the cycle. It ends with ovulation day and begins five days before, as sperm can survive up to five days in the body under the right conditions. Only during these six days is it possible to get pregnant through unprotected sexual intercourse.
When using Natural Cycles for birth control, you will get green days (non-fertile) before ovulation until the algorithm deems it possible that you could be approaching your fertile window. At that point, you will be given red days (days you should use protection like condoms or abstain from vaginal sex) until the algorithm is able to confirm that you have ovulated. The NC° algorithm uses your past ovulation pattern combined with statistical analysis to determine the fertility status at the beginning of your cycle. It will give a buffer of red days before the predicted ovulation based on several factors like sperm survival probabilities, your personal ovulation pattern, how regular your ovulation pattern is, and how much data has been collected from past cycles. NC° Birth Control users will likely get more than six red days per cycle to account for cycle and temperature irregularities. For new NC° Birth Control users, during the first cycles, when the algorithm doesn't have much information on when you usually ovulate and how much that varies, the buffer of red days at the beginning of the cycle is greater.
What about multiple ovulations?
It is possible to have multiple ovulations in one cycle. This happens when both ovaries release an egg cell. In that case, the second ovulation will only happen within 24 hours of the first one.
Read more about multiple ovulations in this article.
What are anovulatory cycles?
An anovulatory cycle is a cycle without ovulation, and most of us will experience it from time to time.
You can read more about anovulatory cycles here, and how the app detects anovulatory cycles here.