When are the infertile days?

Infertile days: when do they occur in the cycle?

The infertile days in a woman’s cycle are the times when fertilisation cannot take place, either because ovulation has not yet occurred or because it is already over. In principle, the female cycle can be divided into three phases:

• the infertile phase before ovulation
• the fertile days around ovulation and
• the infertile phase after ovulation.

The infertile days before ovulation begin on the first day of your cycle (the start of your period). In the first few days, pregnancy is unlikely, but it is not impossible. If your cycles are very short or irregular, you can become pregnant while you are still on your period. In such cases, there are only a few infertile days at the beginning of the cycle.

The usually longer infertile phase comes after ovulation. If no fertilisation has taken place, the so-called luteal phase begins. It usually lasts 10 to 16 days until the next period. During this phase, conception is no longer possible; this phase is considered reliably infertile.

Infertile days at the beginning of the cycle

The first phase of infertile days begins with your monthly period and ends up to five days before ovulation. The fertile days result from how long the egg can be fertilised and from the lifespan of sperm. Sperm can survive for up to 5 days in a woman’s body.

Infertile days after the day of ovulation

After the days on which fertilisation is possible, the next infertile phase begins. It does not start directly with ovulation, because the egg can still be fertilised for up to 24 hours. Once ovulation has taken place, however, you can regard the days from two days later until the start of the next cycle as infertile. The infertile days in the second half of the cycle can last 10 to 16 days.

Calculating the infertile days: here is how it works!

With natural methods such as natural family planning (NFP), you can reliably calculate how many infertile and fertile days you have in each cycle. It is best to use a method that bases its calculation on a combination of two body signs.

The symptothermal method combines two reliable symptoms: the basal body temperature and the cervical mucus. The temperature is regarded as a reliable sign that ovulation has taken place.

The consistency of your cervical mucus, in turn, gives clues about upcoming ovulation. In short, you have one symptom that points to ovulation and one that confirms it afterwards.

The chart below shows the three phases using a 27-day cycle as an example. Here the infertile phases run

• from day 1 to day 11 and
• from day 18 to day 27.

The two curves show the rise in temperature on day 17 and the LH peak on day 15. Just as the cervical mucus reaches its peak before ovulation, so does the hormone LH.

When are the infertile days?

The second infertile phase in the cycle can be determined reliably from the basal body temperature. The infertile phase at the beginning of the cycle, however, is harder to pin down. That is why it is important to track your own cycle regularly.

Calculating the infertile days with cyclotest mySense

With cyclotest mySense, you can analyse two ovulation symptoms:

• basal body temperature and LH or
• basal body temperature and cervical mucus

The great advantage of cycle tracking based on the signs your own body sends out is that every cycle is taken into account, with all its individual features. This is not the case with simple ovulation calculators and calendar apps. They are based on average cycle lengths.

Here too, and all the more so with an irregular cycle, the infertile phase has to be worked out carefully from symptoms you can analyse, because there is no other way of even estimating it. The key point is this: the length and timing of the individual symptoms may change, but the symptoms themselves stay the same and can therefore also be measured.

In addition, factors such as stress, exams, illness or medication can influence your cycles and thus the timing of your infertile phases.