A healthy cycle is a regular cycle, there is no doubt about that. Yet, there is a lot of confusion and unfortunately not always doctors, friends and various algorithms (suprise?!) give clear answers based on the most up-to-date research – let’s remember that until a couple of decades ago the female body was studied very little – and that it is not easy to keep up with the enormous amount of work that doctors have been doing for too many years now; if they don’t speak English, it is even more difficult.

Cycle duration

A healthy cycle lasts between 23 and 35 days. About 60% of women have a cycle between 26 and 30 days (see table 1). But be careful! This applies to those between 25 and 40 years of age.

Table with distribution of cycle length

Source: University of Duesseldorf

From menarche (first menstruation) to about 25 years old

The cycle needs to warm up, and it takes time. This means that it can be normal to have very irregular cycles for about 10 years.

If your cycle skips three months or more, or if at 16 you still haven’t got it, then you have to go to the doctor without delay and without fear, with a bit of diet and lifestyle tips, you can put everything back in place. If they recommend the pill, first read here, get informed, and then make your choice.

After the age of 40 

From about 40 years on, the cycle becomes irregular again. First it will shorten, and then it will lengthen, until it is so long that it never comes back. After 12 months without a cycle, menopause is declared, which happens around the age of 50 (in European women). Menopause is a milestone, as is the menarche. Those who have had their last cycle (called menopause) are post-menopausal. I trust that our great-granddaughters will find a good name for this magical moment in a woman’s life, because in the meantime society will have changed so much that we would hardly recognize it.

Changes in menstrual cycle duration

The more regular it is, the better, because it means that body and mind are in a state of balance. However, it is wrong to think that a few days difference in cycle duration are always an indication of imbalances or problems.

A study of 210 women (see Table 2), followed for 12 months, showed that only 3.3% of them had minimal variations – from 1 to 3 days over 12 months. The majority, 52.9% had variations from 4 to 9 days over 12 months.

Table of cycle length

Source: University of Duesseldorf

Is your period late?

First of all, let’s dispel one myth: we have the cycle every day. Menstruation is just one part of it. We all know, but it’s good to remember it.

Now, let’s face another myth: menstruation is never late; it is ovulation that has been delayed.

Menstruation will always arrive on time 12-16 days after ovulation – but for each of us that number is constant – for me, modestly, it is always 13*.

Your period comes later than you expected every time ovulation is postponed, suspended or suppressed. Our bodies are much more intelligent than we think! Every effort or stressor has the power to suspend the ovulation process, whether it is due to exams, travel, diets or lack of proper nutrition, sports, illness or psychological stress: the last thing the body wants, when it feels unprepared, or under “stress”, is to get pregnant. Not stupid!


The constant luteal phase

Three charts showing the constant luteal phase

Source: Sensiplan Teacher’s Training Book

Here you can see three cycles of the same woman but each with different durations: the first one lasts 23 days, the second 27, the third 33 days. The last phase of the cycle, the one following ovulation and called in the figure “Luteal Phase” is always constant (11 days). What changed was the yellow-colored phase in the figure, the Follicular Phase, which precedes ovulation.

How do you calculate your next period?

It’s really very simple, you have to measure your  basal body temperature for three minutes, as soon as you wake up.

Many myths dispelled

To conclude, we are taught that a regular menstrual cycle should last 28 days and should always be exactly 28 days. This is a myth that contains a grain of truth. The more regular, the better, but delays can be read as a defense mechanism, and not necessarily as an illness or a reason for major alarm. The majority of women have a cycle duration that is more or less 29 days, but cycle length varies with age. Too many young women are given the pill for irregular cycles. The pill does not regulate the cycle, and the young cycle needs its own time to find its own rhythm.




*13 is an esoteric number, the number associated with the Moon and the female. Thirteen are the moons in a year, 13 is the number of menses if each cycle lasts between 26 and 30 days. Friday 13 is the day sacred to the female deity, since many millennia, in Northern Europe (ah-ha!).