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Menstrual Cycle Calculator

Predicts the date of your next period based on your last cycle. Free, instant and no sign-up required.

Predicted next period

How does the menstrual cycle calculator work?

The menstrual cycle is the time between the first day of your period and the first day of your next period. On average, it lasts 28 days, but it can vary between 21 and 35 days depending on the person. Our calculator uses the date of your last period and your usual cycle length to estimate when your next menstruation should begin.

The 4 phases of the menstrual cycle

Your cycle is divided into four distinct phases: the menstrual phase (period), the follicular phase (preparation for ovulation), ovulation (release of the egg) and the luteal phase (preparation for potential menstruation). Understanding these phases helps you better anticipate the physical and emotional changes you experience each month, such as variations in energy, mood or skin.

Why track your menstrual cycle?

Tracking your menstrual cycle helps you anticipate your period and better plan your daily life. It also allows you to identify potential irregularities that might require medical consultation. Regular tracking is also useful for understanding your fertility window, managing premenstrual symptoms and adapting your diet and physical activity to each phase of your cycle.

Calculation limitations and when to consult

This calculator provides an estimate based on a regular cycle. If your cycles vary greatly in length, the results will be less accurate. Factors such as stress, travel, weight changes or certain medications can affect your cycle regularity. If you notice persistent irregularities, bleeding between periods or unusual pain, we recommend consulting a healthcare professional.

Frequently Asked Questions

How do I calculate the date of my next period?
To calculate the date of your next period, note the first day of your last period and add your average cycle length (usually between 21 and 35 days, with an average of 28 days). The result is the estimated date of your next menstruation. Our calculator does this automatically and also shows predictions for the next 2 cycles.
What is the normal length of a menstrual cycle?
A normal menstrual cycle lasts between 21 and 35 days. The average is 28 days, but every woman is different and your own "normal" may vary. A cycle is considered irregular if its length varies by more than 7 days from one month to the next. Teenagers and women approaching menopause often have more irregular cycles.
Why is my cycle irregular?
Irregular cycles can be caused by stress, significant weight changes, intense physical exercise, hormonal disorders (such as polycystic ovary syndrome), perimenopause, or certain medications including hormonal contraception. If your cycles are regularly irregular, it is recommended to consult a gynecologist.
Is this calculator reliable for predicting my period?
This calculator provides an estimate based on your cycle regularity. The more regular your cycle, the more accurate the prediction. For more personalized tracking that adapts to your data over time and takes your symptoms into account, download the Rythia app which uses artificial intelligence for increasingly accurate predictions.

Related Tools

Ovulation Calculator Fertility Calculator Symptom Checker

This tool provides indicative estimates and does not replace medical advice. Consult a healthcare professional for any questions.

For complete tracking, download Rythia

Personalized AI predictions, daily briefings and tailored support for your menstrual cycle.

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