How the Menstrual Cycle Works, And What Your Body Is Telling You Each Month

Understanding how the menstrual cycle works goes far beyond knowing when your next period is due. Every month, your body moves through a carefully timed sequence of hormonal shifts that affect your energy, mood, skin, digestion, and fertility. Most of us learned the basics in school, but very few of us were taught what's happening and why it matters.

This guide breaks it down clearly: the phases, what's normal, what isn't, and when it's worth speaking to a doctor.

What Is the Menstrual Cycle?

The menstrual cycle is a monthly process driven by a complex interplay of hormones produced and regulated by the hypothalamus, pituitary gland, and ovaries. It's not just about your period, that's only the most visible part. Beneath the surface, your body is constantly preparing, releasing, and renewing.

Your cycle begins on day 1 of your period and ends the day before your next one starts. While the average length is 28 days, anything between 24 and 38 days is considered normal.

What Does a Normal Menstrual Cycle Look Like?

According to the International Federation of Gynaecology and Obstetrics (FIGO), a normal cycle is defined by four key features: frequency, regularity, duration, and flow volume.

Frequency: Cycles should occur every 21 to 35 days. Cycles shorter than 21 days are called polymenorrhea (too frequent), while those longer than 35 days indicate oligomenorrhea (infrequent periods). If bleeding stops altogether for several months, that's amenorrhoea, a sign that needs medical evaluation.

Duration: Normal period bleeding lasts between 2 and 8 days. Longer than that may point to hormonal imbalance, fibroids, or other gynaecological causes.

Flow volume: There's no universal standard, since flow varies widely. Medically, heavy menstrual bleeding is defined as blood loss above 80mL per cycle, roughly soaking through a pad or tampon every 1–2 hours for several consecutive hours. That said, the American College of Obstetricians and Gynecologists (ACOG) now defines "heavy" by impact, not volume: if your bleeding disrupts daily life, sleep, or social activity, it's worth discussing with a doctor.

Regularity: FIGO considers a cycle regular when the difference between your shortest and longest cycles stays within about 7 days. For younger women or those approaching menopause, a slightly wider variation of up to 9–10 days is still considered normal.

Light bleeding (under 5mL per cycle) is rarely a concern on its own, though it can occasionally indicate cervical stenosis or uterine scarring. Hormonal contraceptives, thyroid conditions, and stress can all quietly shift your bleeding patterns over time.

The Four Phases of the Menstrual Cycle

The menstrual cycle is made up of two overlapping cycles: the ovarian cycle (what happens in your ovaries) and the endometrial cycle (what happens in your uterus). Together they move through four phases each month.

1. The Follicular Phase (Days 1–14)

The follicular phase begins with your period. During menstruation, your uterus sheds its lining into the blood and tissue you see. You might feel cramps, fatigue, or lower back pain as the uterus contracts to push the lining out.

At the same time, your brain releases FSH (follicle-stimulating hormone) to help your ovaries grow tiny sacs called follicles, each holding an egg. One follicle becomes dominant and starts producing estrogen. As estrogen rises, your mood usually lifts, energy increases, and skin may clear up. Estrogen release is also responsible for a lot of other changes. It rebuilds the uterine lining, makes cervical mucus stretchy and clear. This is the discharge seen when you're ovulating. It's the body's way of making it easier for sperm to reach the egg.

Estrogen also rebuilds the uterine lining and changes the consistency of cervical mucus, making it clear, stretchy, and slippery. This is the discharge many people notice around mid-cycle, and it plays a real role in fertility by making it easier for sperm to travel toward the egg.

2. Ovulation (Around Day 14)

Ovulation is the release of a mature egg from the ovary. It's triggered by a sharp surge in LH (luteinizing hormone) and typically occurs around day 14, though this varies from person to person.

Some people feel a brief, mild pain on one side of the lower abdomen during ovulation, this is called mittelschmerz, and it's completely normal. Estrogen peaks at this point, which is why many people feel their most energetic, social, and confident mid-cycle. This is also the most fertile window of the month.

3. The Luteal Phase (Days 15–28)

After ovulation, the empty follicle transforms into a structure called the corpus luteum, which begins releasing progesterone. This hormone thickens the uterine lining in preparation for a potential pregnancy.

Progesterone has a noticeably different effect on how you feel, it can cause bloating, fatigue, breast tenderness, and emotional sensitivity. If pregnancy doesn't occur, both progesterone and estrogen drop sharply toward the end of this phase, triggering the next period.

4. The Menstrual Phase (New Cycle Begins)

The sudden drop in hormones signals the body to shed the uterine lining. Your period begins, and the cycle starts again. Prostaglandins, chemicals that cause the uterus to contract, rise during this phase, which is what causes cramps. They can also affect the bowels, which is why digestive changes like loose stools or cramping are common in the first day or two of your periods.

Irregular Periods: When Should You Be Concerned?

Some cycle irregularity is normal, particularly in the first few years after getting your period and in the years approaching menopause. But certain patterns are worth paying attention to.

Intermenstrual bleeding: Bleeding between periods, in any amount, is worth flagging. It can be linked to hormonal changes, contraceptive side effects, or benign conditions like cervical polyps, but it sometimes warrants further investigation.

Irregular cycle length: If your cycle length swings by more than 7 days from month to month, or shifts dramatically without explanation, it's worth discussing with a healthcare professional.

When to See a Doctor About Your Period

Some symptoms are easy to dismiss as "just a bad period." These aren't:

Heavy bleeding or clotting (menorrhagia): Soaking through a pad or tampon in under 2 hours, needing to change protection through the night, or passing clots larger than a coin are all signs of menorrhagia and warrant a doctor's visit.

Bleeding between periods: Any intermenstrual bleeding is a red flag for further investigation. Alongside other symptoms, it can indicate uterine or cervical growths, pelvic inflammatory disease, or in some cases, endometriosis (where uterine tissue grows and bleeds in other parts of the body).

Severe diarrhoea: Some digestive sensitivity during your period is normal. But if diarrhoea is severe enough to cause lightheadedness, nausea, or dehydration, or is clearly outside your normal experience, see a doctor.

Multiple missed periods (amenorrhoea) Three missed periods in a row, or no period by age 15, meets the clinical definition of amenorrhoea. Causes include stress, intense exercise, eating disorders, hormonal contraceptives, obesity, PCOS, and certain medical conditions.

Unusual blood consistency: Menstrual blood typically starts bright red and thickens to a darker brown toward the end of your period. Blood that's very watery and pale, or unusually thick throughout, especially when paired with other symptoms like severe cramping or irregular bleeding, should be evaluated.

Severe cramps (dysmenorrhoea): Cramps that become intolerable or interfere with daily life are medically referred to as dysmenorrhoea and are reason enough to see a doctor.

Unusual discharge, fever, or burning when urinating: Infections after periods are more common than most people realise. These symptoms together can indicate an infection that needs prompt treatment to prevent complications.

Conclusion

Your menstrual cycle is one of the most consistent windows into your overall health. Once you understand what's happening in each phase and what normal actually looks like for you, it becomes much easier to spot when something is off. Track from day 1, notice your symptoms, and trust your instincts. If something feels repeatedly wrong, speak with a healthcare professional. The more you understand your cycle, the more confident and in control you feel.

By Peace Chukwu (LinkedIn)
I’m Peace Chukwu, a medical doctor with lots of experience helping young girls and women understand their bodies with clarity and confidence. You can learn more about me here.