Understand everything about the Menstrual Cycle (with calculator)

The menstrual cycle usually lasts about 28 days and is divided into 3 phases, according to the hormonal changes that occur in the woman's body during the month. Menstruation represents the fertile years of a woman's life, which begin in adolescence and last until menopause.

It is normal for the duration of the cycle to vary between 25 and 35 days, but cycles with shorter or longer intervals than these can represent health problems such as polycystic ovaries and, therefore, if this happens it is advisable to consult a gynecologist.

Menstrual cycle calculator

Find out what your menstrual cycle is by entering your data below:


When the menstrual cycle is irregular, it is more difficult to know the day of ovulation and it may be more difficult to get pregnant, as the fertile period cannot be calculated exactly. See how to calculate the fertile period of irregular cycles.

Stages of the normal menstrual cycle

The normal menstrual cycle lasts an average of 28 days, starting on the first day of menstruation and ending when menstruation of the following month begins. Each cycle is divided into 3 phases:

1. Follicular phase

This is the first phase of the cycle, which starts on the first day of menstruation and lasts between 5 to 12 days. At this stage the brain increases the production of follicle-stimulating hormone (FSH), which causes the ovaries to mature their eggs.

With this maturation, the ovary also begins to release greater amounts of estrogen, which is another hormone, responsible for making the lining of the uterus ready for a possible pregnancy.

2. Ovulatory phase

At this stage, estrogen levels continue to rise and cause the body to produce the luteinizing hormone (LH), which is responsible for selecting the most mature egg and getting it out of the ovary, which is when ovulation occurs, usually around day 14 of the cycle.

Once released, the egg travels through the tubes until it reaches the uterus. Normally, the egg survives for 24 hours outside the ovary, so if it comes in contact with sperm, it can be fertilized. Since sperm can last up to 5 days inside the woman's body, it is possible that if the woman had intercourse up to 5 days before ovulation, she could become pregnant.

3. Luteal phase

This phase happens, on average, in the last 12 days of the cycle and, during those days, the follicle, left by the egg inside the ovary, starts to produce progesterone in greater quantity, to continue preparing the lining of the uterus in case of a possible pregnancy. In addition, there is also an increase in estrogen production, so some women may experience breast tenderness, mood swings and even swelling.

When fertilization does not happen, the follicle shrinks inside the ovary and, therefore, the levels of estrogen and progesterone decrease until the lining of the uterus is eliminated, starting menstruation and the next menstrual cycle.

If there is fertilization, the egg is stuck to the walls of the uterus and the body begins to produce hCG, a hormone that keeps the follicle producing estrogen and progesterone at high levels to maintain the lining of the uterus until the placenta forms.

Signs that indicate fertile period

The signs that indicate a fertile period are transparent discharge similar to egg white, increased sensitivity of the breasts and mild pain in the uterus, similar to a mild and transient colic.

In addition to these signs, it is also possible to identify ovulation through the ovulation pharmacy test, such as Confirme and Bioeasy. See how to use these tests to find out if you are in the fertile period.

What makes the menstrual cycle irregular

The irregular menstrual cycle is one in which it is not known when menstruation will come. The most common causes of irregular cycle are:

  • Early fertile life in adolescence, up to 2 years after the first menstruation;
  • Post-pregnancy period;
  • Pre-menopause, due to intense hormonal changes;
  • Eating disorders that cause excess weight loss, such as anorexia nervosa;
  • Excessive physical activity, especially in female athletes;
  • Hyperthyroidism;
  • Polycystic ovary;
  • Change of contraceptive;
  • Stress or emotional disorders;
  • Presence of inflammation, polyps or tumors in the female reproductive system.

In the presence of an irregular menstrual cycle or when the menstrual cycle does not occur for more than 3 months, the gynecologist should be consulted to investigate the cause of the problem. See 10 Menstruation Myths and Truths.