How Long Is a Menstrual Cycle?

For most practical purposes, a woman’s menstrual cycle is assumed to be 28 days long and the duration of menstruation is between 3 and 5 days. This is to say that when we take an average of multiple menstrual cycles, we would get a number in the region of 28 days. However this is not to say that shorter or longer cycles are necessarily abnormal. Depending upon different factors, the length may vary.

It Varies with the Age

When a girl first starts to menstruate, she may have longer and irregular menstruation. At the beginning, the cycles may be as long as 45 days and could be unpredictable. It can take time for the cycle to regularize. Infrequent or irregular cycles are known as Oligomenorrhea. When this occurs in early adolescence, it is not a cause for concern.


For adult women, it can range between 21 days and 35 days. Women around the age of 40 are likely to have the shortest, most regular and most predictable menstrual cycles. When a woman approaches menopause, her cycles may again become unpredictable.

Factors that May Affect the Cycle

Apart from age, there are several other factors that may affect the length of a menstrual cycle:

Anemia: Women who have anemia could have longer, lighter cycles.

Body weight: Women who are overweight, or have certain chronic diseases could also have irregular or unusual cycles.

Body fat: Women with very low body fat percentages – such as competitive female athletes or women with eating disorders – could also have irregular periods.

Hormonal disorders: Hormonal disorders such as Polycystic Ovarian Syndrome (one of the most common reasons for female infertility) can also cause cycles to become irregular and unpredictable. In addition, there could be genetic factors that may result in irregular cycles.

Pelvic diseases: Clotting disorders and pelvic diseases or infections could also cause menstrual irregularity.

Menstrual Problems

Some women experience problems such as amenorrhea which is the absence of periods. Others suffer from menorrhagia which is very heavy and very long periods. Dysmenhhorea is characterized by very painful cramps during periods – this could be due to excessive prostaglandin or due to conditions such as endometriosis or uterine fibroids.

So, How Long Is a Normal Menstrual Cycle?

The point to be remembered when it comes to menstrual cycles is that there is a very wide range of ‘normal’. While for one woman, a 35 day cycle with a 7 day period is perfectly normal, for another woman, a 25 day cycle with a 5 day period may be normal.

The important thing is to know what is ‘normal’ for you by keeping a record of your cycles so that you know when something is abnormal.