How Does The Menstrual Cycle Work? | What Each Phase Does

The menstrual cycle can feel predictable one month and messy the next. That’s normal. A cycle is not a clock; it’s a feedback loop between the brain, ovaries, uterus, and cervix.

Once you know what each phase is doing, symptoms start making more sense. Your notes get clearer, too.

What A Menstrual Cycle Is

A cycle begins on Day 1 of bleeding and ends the day before the next period starts. During that time, an egg matures in an ovary and the uterus builds a lining that could hold a pregnancy.

If pregnancy doesn’t begin, estrogen and progesterone fall near the end of the cycle. The uterine lining breaks down and leaves the body as menstrual bleeding.

Parts That Coordinate The Timing

Four parts do most of the work: the brain, the ovaries, the uterus, and the cervix. They communicate through hormone pulses and tissue changes that repeat in a steady pattern for many people.

The Brain-Pituitary Signal

The hypothalamus and pituitary act like a timing center. They release hormone messengers that tell follicles in the ovaries when to grow and when to release an egg.

The Ovaries And Follicles

Each ovary holds many follicles. In most cycles, a group starts growing and one follicle becomes dominant.

After ovulation, the emptied follicle becomes the corpus luteum. It makes progesterone for the second half of the cycle.

The Uterus And Its Lining

The uterine lining (endometrium) thickens during the first half of the cycle, then shifts into a state that can hold an embryo.

A period is the shedding of that lining. It’s a mix of blood and tissue, not old blood stored for weeks.

The Cervix And Cervical Mucus

Cervical mucus changes texture and amount through the cycle. Near fertile days, it often becomes wetter and stretchier, which helps sperm move.

After ovulation, mucus often turns thicker and tackier.

How The Menstrual Cycle Works In Real Time

Phase names can sound clinical, but the pattern is simple. Bleeding starts the cycle, ovulation follows follicle growth, then progesterone runs the second half until the next period or pregnancy.

Days 1 To 5: Bleeding And Reset

Bleeding begins after estrogen and progesterone drop at the end of the prior cycle. With those hormones low, small vessels in the uterine lining constrict and the lining breaks apart.

Cramps can show up here. The uterus contracts to move tissue out, driven in part by prostaglandins.

Days 1 To 13: Follicular Phase And Lining Build-Up

While bleeding is ending, follicles in the ovaries begin maturing. Follicle-stimulating hormone (FSH) rises early to help that growth.

As follicles grow, estrogen rises. Estrogen rebuilds the uterine lining and often shifts cervical mucus toward a wetter, more slippery feel.

Around Mid-Cycle: Ovulation And Fertile Window

When estrogen rises enough, the pituitary releases a surge of luteinizing hormone (LH). That surge prompts the ovary to release an egg.

The egg enters a fallopian tube. If fertilization doesn’t happen, the egg breaks down and is absorbed.

After Ovulation: Luteal Phase

After ovulation, the corpus luteum makes progesterone. Progesterone changes the uterine lining so it can receive an embryo and stay stable.

If pregnancy doesn’t begin, the corpus luteum breaks down. Progesterone and estrogen fall, and the next period starts.

Hormones That Drive Each Step

Hormones change tissues, fluid balance, and pain sensitivity, which can shift how you feel.

If you want a simple visual of timing, ACOG lays it out in its menstrual cycle infographic.

Estrogen

Estrogen rises during the follicular phase. It thickens the uterine lining and is often linked with clearer cervical mucus.

Progesterone

Progesterone rises after ovulation. It can raise basal body temperature a bit and can affect breast tenderness, digestion, and sleep for some people.

FSH And LH

FSH helps follicles grow early in the cycle. LH surges right before ovulation and is the signal many ovulation test kits detect.

Prostaglandins

Prostaglandins help the uterus contract during a period. Higher levels can mean stronger cramps, nausea, or looser stools around bleeding days.

Cycle Timing Map For Tracking

Cycles vary, so treat this as a map, not a rule. Many people fall in the 24–38 day range. The Office on Women’s Health shares that range in its page on your menstrual cycle.

Cycle Window	Body Changes You Can Notice	What’s Happening Inside
Days 1–2	Heavier bleeding, cramps, tiredness	Hormone drop; lining breaks down and sheds
Days 3–5	Bleeding lightens, cramps ease	New follicles grow; lining starts rebuilding
Days 6–9	More energy for some, less pelvic heaviness	Estrogen rises; endometrium thickens
Days 10–13	Wetter mucus, higher libido for some	Dominant follicle matures; estrogen peaks
Ovulation Window	Possible one-sided twinge, slippery mucus	LH surge; egg released into the tube
Early Luteal	Basal temperature rises; mucus thickens	Corpus luteum forms; progesterone climbs
Mid Luteal	Breast tenderness, bloating, steadier mood	Progesterone holds the lining in place
Late Luteal	Cravings, irritability, spotting for some	Corpus luteum fades; hormones fall

What You Might Notice In Your Body

Some people feel clear shifts across the month. Others feel almost the same week to week. Symptoms can change with sleep loss, illness, travel, or new training plans.

Bleeding, Clots, And Cramps

Flow can range from light to heavy. Small clots can happen on heavier days since blood can pool before leaving the body.

Occasional cramps are common. Pain that keeps you from school, work, or sleep deserves medical attention.

Mucus And Discharge

Cervical mucus often shifts from dry or sticky to wetter and stretchy, then back to thicker and tackier after ovulation.

Itching, burning, strong odor, or green-gray discharge can signal infection. Contact a clinician if that shows up.

PMS-Type Changes

Some people notice mood shifts, headaches, acne, breast tenderness, or bloating in the late luteal phase. Tracking timing can show whether symptoms repeat in the same window each cycle.

If symptoms disrupt daily life, talk with a clinician about options.

Tracking That Stays Useful

Tracking should answer a question and stay easy to maintain. Pick one or two signals and stick with them for a few cycles.

Calendar Notes

Mark Day 1 as the first day of bleeding. Track the last day of bleeding too, since duration can matter in a medical visit.

Basal Body Temperature

Basal body temperature is your waking temperature taken before you get out of bed. Progesterone after ovulation often raises it a bit.

This method is most reliable when sleep timing is steady and the thermometer is consistent.

Cervical Mucus Notes

Write down what you notice: dry, sticky, creamy, watery, stretchy. The wetter and stretchier days often line up with fertile days.

Check at the same time each day, since showering, sex, and arousal can change what you notice.

Ovulation Test Strips

These look for the LH surge in urine. A positive test suggests ovulation is close, not that it already happened.

The NICHD breaks down cycle timing in plain steps in its menstruation fact sheet, which can help you match your notes to what’s happening inside.

Tracking Tool	Best Use	Common Pitfall
Calendar	Period timing and cycle length	Assumes ovulation happens on the same day each cycle
Basal temperature	Confirms ovulation happened	Sleep changes and alcohol can blur the pattern
Cervical mucus	Finds fertile window earlier	Infections or antihistamines can change mucus
LH test strips	Predicts ovulation timing	Hard to read with irregular surges
Symptom log	Links cramps, headaches, acne, mood	Patterns hide when dates are missing

Why Cycles Change

A “late” period often means ovulation happened later than usual. Since the luteal phase tends to be steadier than the follicular phase, a delayed ovulation is a common reason cycles stretch longer.

Travel across time zones, sleep loss, rapid weight change, and intense training can shift ovulation timing. Some medications can change bleeding too.

Teens And Early Cycles

In the first years after the first period, cycles can be irregular. The brain-ovary signaling loop is still settling in.

Perimenopause And Midlife Changes

In the years leading up to menopause, cycles can shorten or lengthen, and ovulation may not happen every cycle. Bleeding that is heavy, frequent, or paired with pain should be checked.

When To Call A Clinician

Some variation is normal. Still, certain patterns can signal a condition that needs diagnosis and treatment.

• Bleeding that soaks through pads or tampons quickly for several hours
• Bleeding between periods or after sex
• Periods that stop for three months or more when pregnancy isn’t a factor
• Pelvic pain that keeps you from daily activities
• Lightheadedness, fainting, or symptoms that suggest anemia

ACOG lists warning signs and evaluation steps in its page on heavy and abnormal periods.

Comfort Moves That Often Help

If your periods are uncomfortable but not alarming, small changes can make the days smoother. Try one change for one cycle, then keep what works.

Heat And Gentle Movement

A heating pad on the lower belly can ease cramps. Light movement like walking can relax pelvic muscles and improve blood flow.

Sleep And Recovery

Short sleep can raise pain sensitivity and make headaches or irritability feel worse. If you can, protect your sleep window during bleeding days.

Medication Basics

Over-the-counter anti-inflammatory medicines can reduce cramps for many people. Follow label directions and avoid them if you have kidney disease, stomach ulcers, or a clinician has told you not to take them.

If pain is strong or bleeding is heavy, prescription options and hormonal methods can reduce symptoms.

Reading Your Next Cycle With Less Guesswork

The cycle is a coordinated sequence: follicles grow, estrogen rebuilds the lining, an LH surge releases an egg, and progesterone steadies the second half.

Tracking one or two signals can turn vague symptoms into a clear timeline. If a pattern shifts sharply or symptoms interfere with daily life, a clinician can help you sort out the cause and choose treatment.