Menstrual cycle: how to count it and what duration is normal

The menstrual cycle, or period cycle, is not only the days of bleeding themselves, but the entire monthly process during which the body prepares for pregnancy. Understanding how to count the cycle and which numbers are considered normal helps you notice changes more calmly and discuss them with a doctor in time.

What the menstrual cycle is

Every month the body prepares for a possible pregnancy: hormone levels change, the lining of the uterus thickens, and an egg matures. If pregnancy does not occur, the functional layer of the endometrium is shed — this is how menstruation begins. Bleeding usually lasts from 2 to 7 days, on average about 5 days, and the heaviest days are the first two. About 1–5 tablespoons of blood are lost during menstruation. The cycle is divided into phases: menstrual, proliferative and secretory — according to changes in the uterus, or follicular, ovulatory and luteal — according to changes in the ovaries.

How to count the menstrual cycle

The first day of the menstrual cycle is the first day of menstruation, not the last. You need to count from the first day of one menstruation to the first day of the next. For example, if bleeding began on March 1 and the next on March 29, the cycle length is 28 days. To see your own normal, it is useful to note several cycles in a row: the start date, the duration of bleeding and its character. This way you will see your individual rhythm rather than comparing yourself with a conventional "ideal".

• the first day of bleeding;
• the duration of menstruation;
• the heaviness of bleeding;
• painful sensations;
• bloody discharge outside of menstruation.

What cycle duration is considered normal

The average menstrual cycle length is about 28 days, but this is not the only normal option. The normal menstrual cycle in an adult woman is from 21 to 35 days. In young women whose periods are just becoming established, the range is wider — from 21 to 45 days. Cycles can be shorter or longer than 28 days and still remain normal. The duration of menstruation itself is from 2 to 7 days, usually about 5 days. Regularity says more than an exact match with 28 days; if your cycle consistently fits within its own range, this may be your normal.

Short and long cycle: 21, 22 and 35 days

A 21-day cycle is the lower limit of normal for an adult woman. 22 days between periods also falls within the usual range of 21–35 days. A 35-day cycle is the upper limit of normal; if it is consistently like this, it is not necessarily a disorder. It makes sense to discuss with a doctor a situation where the cycle has become shorter than 21 days or longer than 35 days, as well as if it has changed sharply compared with your usual rhythm. In young women, a cycle of up to 45 days may be a variant of normal, but a persistent deviation from this range requires evaluation.

What is considered a menstrual cycle disorder

Menstrual cycle disorders are changes in the usual rhythm: delays, irregular periods, very heavy bleeding. These include amenorrhea — absence of menstruation; oligomenorrhea — periods less often than usual; menorrhagia — very heavy bleeding; prolonged bleeding if menstruation regularly lasts longer than 8 days; dysmenorrhea — painful menstruation with pronounced cramps. The causes vary: hormonal fluctuations in adolescence, pregnancy, changes after childbirth and breastfeeding, the influence of hormonal contraception, the menopause period. Bloody discharge between periods, after sex or after menopause also requires checking.

When to see a doctor

See a doctor if you notice pronounced changes in your cycle, very heavy bleeding or severe pain. A reason for consultation is a regular bleeding duration longer than 8 days, a cycle shorter than 21 or longer than 35 days in an adult woman, as well as bloody discharge outside of menstruation. The doctor will assess the history, rule out pregnancy and, if necessary, prescribe examinations, for example hormone level tests — FSH, estradiol, anti-Müllerian hormone. This helps to understand the cause of the disruption and choose further management.

A cycle disorder by itself is not a reason to call an ambulance. 103 or 112 — if against the background of bleeding you lose consciousness or have very heavy bleeding.

This material is for reference: it helps to make sense of the numbers and notice changes, but does not replace a doctor's consultation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer