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Menstrual Cycle Calendar Calculator

Reviewed by MD Katiuska Ríos Calderón

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When did your last period start?

Average length of your menstrual cycles:

Average duration of your menstruations:


Pre-period days
Days of the period
Post-period days
Ovulation day (very fertile)
Most fertile days

Optimal fertility period:

  • From to

More details of interest:

  • Approximate ovulation date:
  • Approximate date of the next menstruation:
  • If you become pregnant during this period, the due date could be:

Related Resources

Table of Contents

How to Use the Menstrual Cycle Calculator

To use our online menstrual calendar calculator, indicate the first day of your last period and how many days your cycles and bleeding usually last.

Once you have indicated both, click on "Calculate".

What is the Menstrual Cycle

Many women do not have complete information about their menstrual cycle and often wait to become moms (or try to) to start getting to know it.

A woman begins to menstruate when she reaches puberty. From that moment, she has the ability to become pregnant, which is why it is important to know the following.

What is really the menstrual cycle?

It is the set of mechanisms that prepare the ovary for ovulation and a possible pregnancy.

This process is carried out under the control of the hypothalamus and pituitary gland, in this case, we are talking about an axis, the hypothalamus-pituitary-ovary axis.

This process is controlled by two hormones: the follicle-stimulating hormone or FSH and the luteinizing hormone or LH.

The entire menstrual cycle usually lasts between 21 and 35 days, and is divided into three phases.

The Follicular Phase

Begins on the first day of menstruation.

Here, FSH stimulates the growth of several follicles, but only one of them will mature and is called the dominant follicle and will be the one to produce and release an egg.

This follicle produces estrogens to prepare the endometrium and to make changes in the cervical mucus and favor the ascent of sperm.

The Ovulatory Phase

In this phase, the level of LH increases to its maximum level, the egg finishes maturing, the follicle breaks and finally the egg will be released to be fertilized.

In a 28-day cycle, this can occur between day 12 and 14 of the same.

The Luteal Phase

This phase begins immediately after ovulation.

The follicle that released the egg undergoes a process of transformation, becoming the corpus luteum, which produces a hormone called progesterone.

This hormone conditions the uterus for the embryo to nest or implant.

If there was no fertilization, then the endometrium will shed and menstruation will occur between day 28 to 30 of the cycle.

The premenstrual syndrome occurs during the luteal phase.

How to Calculate the First Day of the Menstrual Cycle

Normally, menstruation arrives every 21 -35 days for adult women and every 21-45 days in adolescents.

It starts counting from the first day of menstruation until the first day of the following one.

Previous Concepts

The menstrual cycle is linked to the constant oscillation of estrogen levels, especially in the follicular phase, as we have told you before.

In the ovulatory phase, the egg reaches the fallopian tubes, this phase is the ideal time to become pregnant.

If the egg is not fertilized in this period, the levels of progesterone and estrogens drop. Therefore, the uterus loses its lining during this last luteal phase.

Once you have a clear understanding of the phases of the cycle, you can start making decisions related to your health or family planning.

How to Perform the Calculation

To know the approximate first day of your menstruation, and, consequently, know how long the cycle will last, you should start counting what is the first day of the cycle and calculate how many days separate it until the beginning of the next cycle.

The first day of your ovarian cycle corresponds exactly to the first day of your menstruation, therefore, note it down to remember it.

The bleeding period, as a general rule, lasts between 3 and 5 days, but it can vary depending on each case.

On the seventh day of menstruation, vaginal bleeding should have ended, and the ovary would start its process of forming the preovulatory follicles.

This is the main cause of the increase in estrogens that usually takes place between the fourth and seventh day.

What are the Usual Values

Most adult women have a menstrual cycle every 28 days, as a general rule, that is, this is the difference in days between one cycle and another.

However, menstruation can be extended or shortened within a range of 21 days to 35.

As this can vary, it is important that you note, at least for three consecutive cycles, how often your menstruation comes.

On the other hand, if you are taking the contraceptive pill, as a general rule, the cycle should always be 28 days, since the treatment includes 21 contraceptive pills and 7 placebos.

If, on the other hand, you are taking some type of hormonal treatment, the cycles tend to come less frequently.

As long as you stay within the previously mentioned ranges, you should not have any problem with your menstruation, even so, never stop making periodic visits to your specialist so that they can advise you with more certainty.

How to Track Cycles

As for the method of control, you can use the more traditional methods, such as noting it on the calendar or a paper by hand, or, even, the more modern ones such as the various smartphone applications created for this purpose.

Once you have noted the days, you will be able to anticipate when your own cycle should start.

For example, if the cycle comes to you regularly every 28 days, calculate when the next one will be so you can establish if it comes late or early.

How to Know if I Have My Period

Many women start to show menstrual symptoms even days before, but in the short term, these symptoms begin to disappear.

These premenstrual symptoms usually appear from day 20 to day 22 of the cycle. This is known as premenstrual syndrome.

Premenstrual Syndrome Symptoms

Each woman may present different effects during the premenstrual syndrome with its particularities, which can be both physical (weight gain, fatigue, drowsiness) and psychological (irritability, sadness or premenstrual dysphoric syndrome).

Other common symptoms are gastrointestinal problems: you might notice your abdomen more bloated than usual or diarrhea before your menstrual cycle starts. One way to avoid or control this is to decrease salt consumption from day 15 to 18 of the cycle.

You might also start to notice changes and pains in your body, such as muscle or breast pain, in both cases, an anti-inflammatory can be the solution.

Acne is another symptom that is often suffered in the days preceding menstruation.

To combat mood changes, it is advisable to do 30 minutes of physical activity with a rather moderate intensity, so you could help yourself feel better and try to improve those small downturns you suffer.

These symptoms should last a maximum of 4 to 5 days, and should have disappeared when vaginal bleeding begins.

It's important to make periodic visits to your specialist, but if you start to notice too strong pains or that the previous symptoms last too long, you should make an extraordinary visit.

We hope the article has been to your liking and that you have been able to learn these useful tips that help you better face your period, we also hope you make good use of the period calculator, if so do not hesitate to share this article on your social networks.

Lastly, if you find any errors in the programming of the menstrual calculator or in the content of the article, let us know through the contact page, so we can improve this community of free tools and simulators every day.

  • Chemical Biological Institute. (2018). PREMENSTRUAL SYNDROME AT IQB. [online] Available:
  • Mayo Clinic. (2018). Menstrual cycle: what's normal, what's not. [online] Available at:
  • (2018). Premenstrual Dysphoric Disorder. [online] Available at:
  • National Institute of Educational Technologies and Teacher Training. Biosphere Project. (2018). Human Reproduction. [online] Available at:
MD Katiuska Ríos Calderón
Doctor of Medicine and Surgery from UCLA. Specialized in Gynecology and Reproduction. Subspecialized in Endocrine Gynecology and Climacteric.
Dr. Katiuska Ríos Calderón holds a degree in Medicine from the Universidad Centr... Read more »

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