How to know if you are fertile: cycle, ovulation and signs to know

How the cycle works

The menstrual cycle is counted from the first day of a period to the first day of the next, and usually lasts 21 to 35 days. It includes a follicular phase of variable length, ovulation, then a luteal phase of about 12 to 14 days, which is more stable.

It is the variability of the first phase that explains why ovulation does not necessarily fall “on day fourteen”.

The fertile window

The fertile window covers about six days per cycle: the five days before ovulation and the day of ovulation itself. Sperm can survive several days in cervical mucus, whereas the egg can only be fertilised for roughly 12 to 24 hours.

In practice, intercourse every two to three days throughout the cycle covers this window without having to calculate it precisely.

Commonly used signs of ovulation

Several self-observation markers are used:

• cervical mucus, which becomes more abundant, clear and stretchy as ovulation approaches,
• a slight rise in basal body temperature, of about 0.3 to 0.5 °C, occurring after ovulation,
• sometimes a brief one-sided pelvic pain, or breast tenderness.

What self-observation does not tell you

These markers help locate ovulation, with a margin of error, and are useful for timing intercourse. They say nothing about ovarian reserve, tubal patency or semen quality, and have no diagnostic value.

Only a medical assessment documents fertility: semen analysis in men, hormone tests, pelvic ultrasound and tubal evaluation in women. It always concerns both partners.

When to ask for that assessment

The usual thresholds apply: 12 months of unsuccessful attempts, or 6 months from age 35, and earlier in the presence of very irregular cycles, significant pelvic pain or a known medical history.