A menstrual cycle begins on the day you get your period and ends the day before your next period starts.

The average menstrual cycle is 28 days long, meaning there are 28 days from the first day of one period until the next period begins. Ovulation usually occurs 14 days before the next period, which would be on day 14 in an average 28-day cycle. It is normal for a cycle to range between 23 and 35 days. If your menstrual cycle is consistently longer or shorter for several months, we recommend contacting your doctor.

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How do you count the number of days in your menstrual cycle?

To count the days in your menstrual cycle, start from the first day of your last period and count up to the day before your next period begins. This will give you the total number of days in that cycle. Using the calendar method or an app can make it easier to track your cycle. After monitoring your menstrual cycle for about 3 months, you can see if the number of days is consistent each month or if there is a significant variation in duration.

Try our menstrual calculator in this article.

See the 4 phases of your cycle

A typical menstrual cycle consists of 4 phases, where sex hormone levels fluctuate continuously, something many women notice both physically and mentally.

Menstrual Phase

The menstrual cycle begins on the first day of menstruation, marking the start of the menstrual phase, which typically lasts 3-5 days. During this period, the ovaries produce very little estrogen and no progesterone. Many women experience menstrual cramps, sore breasts, and often feel tired and low on energy.

Follicular Phase

After menstruation, estrogen levels gradually rise, which often brings renewed energy and an improved mood. Many women also experience an increased sex drive, which is natural as the body prepares for ovulation around day 14 in a 28-day cycle. In this phase, fertility is high, and intercourse can lead to pregnancy.

Ovulation Phase

Shortly before ovulation, the production of FSH decreases, while LH levels increase. This causes the mature follicle to release the egg, marking ovulation, and the woman is now at her most fertile. If you use an ovulation test, it will be positive at this time. The egg survives for 24 hours, but since sperm can live up to 6 days, intercourse in the days leading up to ovulation can also lead to pregnancy.

Read more about ovulation and calculate when your next ovulation will occur with our ovulation calculator.

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Luteal Phase

The final phase of the cycle, the luteal phase, lasts from ovulation until the next menstruation – unless pregnancy occurs. In the days leading up to the next period, both estrogen and progesterone levels drop. This can lead to symptoms of premenstrual syndrome (PMS).

Frequently Asked Questions About the Menstrual Cycle

How many days does a normal menstrual cycle last?

An average menstrual cycle lasts 28 days, but it can range from 23 to 35 days. The cycle length may also vary slightly from month to month.

How long does a menstrual cycle need to be to be considered regular?

A menstrual cycle is considered regular if it is roughly the same length each month. Typically, a regular cycle falls between 23 and 35 days.

When is a menstrual cycle considered irregular?

A menstrual cycle is considered irregular when there are significant differences in the number of days it lasts from month to month. For example, if your cycle is sometimes 25 days and other times 35 days, it is considered irregular. A cycle is also irregular if it is shorter than 23 days or longer than 35 days, as this falls outside the range of what is considered a regular cycle. If menstruation often skips several months or if the number of bleeding days varies significantly, it may also be a sign of an irregular cycle.

How many days does menstruation usually last?

Menstrual bleeding usually lasts 3-7 days. However, this can vary from person to person, and it is completely normal if your bleeding is shorter or longer.

Which days in the menstrual cycle are the most fertile?

The most fertile days are typically in the middle of the woman’s menstrual cycle, around days 10-16 in an average 28-day cycle. Fertility peaks at ovulation, which usually occurs around day 14 of the cycle.

Can the length of the menstrual cycle change?

Yes, the length of the menstrual cycle can change multiple times throughout life. Factors such as stress, weight changes, hormonal shifts, or illness can affect the number of days in your cycle. As you approach menopause, cycles typically become longer.

Sources: Sundhed.dk, Rigshospitalet