Your menstrual cycle is the roughly monthly hormonal rhythm that readies your body for a possible pregnancy. It is also a useful health signal — and it changes through your 30s, 40s, and the years around menopause.
What is the menstrual cycle?
A cycle is counted from the first day of one period to the day before your next period starts. A "typical" cycle is often described as 28 days, but that figure is an average, not a rule. Anything roughly 21 to 35 days, with 2 to 7 days of bleeding, is commonly normal. Cycle length varies between people and from month to month in the same person, and that variation is usually nothing to worry about.
Behind the scenes, the brain and ovaries talk to each other through hormones. The pituitary gland releases FSH (follicle-stimulating hormone) and LH, while the ovaries produce estrogen and progesterone. The rise and fall of these hormones is what creates the phases below.
The menstrual cycle phases
Most cycles move through four overlapping phases. Because the timing is anchored to ovulation rather than a fixed calendar, the simplest way to place ovulation is to count back about 14 days from your next period. The day numbers below assume a 28-day cycle, so treat them as a guide that shifts with your own cycle length, not a fixed timetable.
| Phase | Typical timing (28-day cycle) | Main hormones | What's happening |
|---|---|---|---|
| Menstrual (period) | Days 1–5 | Estrogen and progesterone low | The womb lining sheds as bleeding because no pregnancy occurred. |
| Follicular | Day 1 to ovulation | FSH rises, then estrogen rises | Follicles in the ovary mature and the womb lining thickens again. |
| Ovulation | About 14 days before your next period (around day 14 in a 28-day cycle) | LH surge, estrogen peak | An egg is released — see ovulation. This is the most fertile window. |
| Luteal | Ovulation to the next period (about 12–14 days) | Progesterone rises, then both fall | The lining is maintained; if there's no pregnancy, hormones drop and a period begins. |
The follicular phase
The follicular phase starts on the first day of your period and runs until ovulation. Rising FSH prompts several ovarian follicles to grow, and the dominant one produces increasing estrogen, which rebuilds the womb lining. This phase varies most in length from cycle to cycle, which is the main reason overall cycle length differs and why ovulation does not always land on day 14.
The luteal phase
After ovulation, the emptied follicle becomes the corpus luteum and releases progesterone, which steadies the lining for a possible embryo. The luteal phase is more consistent, usually around 12 to 14 days. As progesterone and estrogen fall at the end, some people notice premenstrual changes — see our guide to PMS and PMDD.
The hormones driving your cycle
- Estrogen builds the womb lining and peaks before ovulation. It also affects mood, sleep, and energy.
- Progesterone rises after ovulation to prepare and maintain the lining.
- FSH from the pituitary recruits and matures ovarian follicles early in the cycle.
- LH surges mid-cycle to trigger the release of the egg.
When these hormones fluctuate — naturally, or because of a condition — your cycle length, flow, and symptoms can shift.
Period cramps: why they happen and what helps
Mild to moderate cramping with your period is common. As the lining sheds, the womb releases hormone-like chemicals called prostaglandins that make the muscle contract and squeeze blood vessels, which is what you feel as cramps — a normal pattern doctors call dysmenorrhea. For everyday relief, many people find that a heat pad or warm bath, gentle movement, and over-the-counter anti-inflammatory pain relievers (NSAIDs such as ibuprofen) help, because NSAIDs lower prostaglandin levels. Always follow the label and pharmacist advice on whether a medicine is suitable for you. Pain that disrupts your daily life, or that is getting worse, is different — see period pain and the red flags below.
How to track your cycle (and why it helps)
Tracking turns a vague sense of "off" into useful information you can share with a clinician. You can use a paper calendar, a notes app, or a period-tracking app. Helpful things to record:
- The first day of each period (this starts a new cycle).
- How many days you bleed and how heavy the flow is.
- Symptoms such as cramps, mood changes, breast tenderness, or spotting.
- Any bleeding between periods or after sex.
Over a few months, patterns emerge — your usual cycle length, your normal flow, and your typical symptoms. That personal baseline makes it easier to spot a meaningful change. Tracking the days around ovulation also helps you understand your fertile window.
How cycles change in midlife and perimenopause
From your late 30s onward, hormone levels begin to fluctuate. In perimenopause, cycles often shorten first, then become irregular — closer together, further apart, lighter, or heavier — as ovulation becomes less predictable. This is a normal part of the transition, not a sign something is wrong. For what to expect, see irregular periods in perimenopause and the broader perimenopause symptoms.
Contraception still matters here. Irregular cycles do not mean you can no longer get pregnant — ovulation can still happen unpredictably during perimenopause, so if you want to avoid pregnancy you still need contraception. As a general guide, it is usually advised until 12 months after your last period if you are over 50, or 24 months if you are under 50; a clinician can confirm what is right for you.
Periods eventually stop altogether. Menopause is confirmed once you have gone 12 months with no period.
When variation points to a condition
Some cycle changes are worth investigating rather than waiting out. Polycystic ovary syndrome (PCOS) can lengthen cycles or cause them to be skipped because ovulation is irregular. Thyroid problems, stress, significant weight change, and certain medications can also disrupt the cycle. Heavy or prolonged bleeding can lead to iron-deficiency anemia, so it is worth raising with a clinician if your periods are heavier or longer than your normal.
What's normal vs. what to check
Use your own tracked baseline as the reference point. Reassuringly, a lot of variation is normal — but a few signs deserve prompt attention.
| Commonly normal | Worth getting checked |
|---|---|
| Cycle length of about 21–35 days | Cycles consistently shorter than 21 or longer than 35 days, or very irregular |
| 2–7 days of bleeding | Bleeding more than 7 days, or soaking a pad or tampon every hour for several hours, large clots, or "flooding" |
| Mild cramps eased by heat or NSAIDs | Pain that disrupts your daily life or is getting worse |
| Cycle changes during perimenopause | Any bleeding 12+ months after your last period |
When to see a clinician
These guides are educational and not a diagnosis. See a clinician if you notice any of the following, and seek urgent care for severe or sudden symptoms:
- Any bleeding after menopause. Vaginal bleeding 12 or more months after your last period is not normal and should be checked promptly — it can occasionally signal endometrial (womb) cancer, so never dismiss it.
- Very heavy bleeding. Soaking through a pad or tampon every hour for several hours, passing large clots, or "flooding" — see heavy periods. Extreme tiredness, breathlessness, or looking pale can mean anemia and needs care, because heavy periods can cause iron-deficiency anemia.
- Bleeding between periods or after sex, or periods suddenly much heavier or longer than your normal.
- Severe period pain that disrupts your life. This is not something to just endure — it can point to endometriosis, fibroids, or adenomyosis. Sudden severe pelvic pain, pain with fever, or pain when pregnancy is possible (a possible ectopic pregnancy) needs urgent care.
- Severe premenstrual symptoms that affect your mood or daily life may be PMDD, a real condition rather than "bad PMS." Any thoughts of self-harm need urgent help right away.
Tracking your symptoms and bringing the record to your appointment helps your clinician find the cause faster.
