Menstria · everything menstrual
Your period, from the first one to the last.
Menstruation is not one event that repeats for thirty-odd years and then stops. It is a system that starts, settles, varies, changes and ends — and every stage has its own version of normal. Menstria explains each stage in plain language and gives you free tools to check where you actually are.
Nothing you enter leaves your browser. Every threshold on this site traces to a named publication, not to a guess.
Get help now — before using anything on this site — if:
- you are soaking through a pad or tampon every hour for two hours in a row;
- you feel faint, dizzy or breathless, or your heart is racing;
- you are pregnant, or might be, and you are bleeding;
- you have any vaginal bleeding at all after menopause.
The basics
The cycle and the period are not the same thing
Almost everyone uses these two words interchangeably, and almost every misunderstanding about menstrual health starts there. They describe different things, on different timescales.
The menstrual cycle
The whole repeating process. Counted from the first day of one period to the day before the next. It includes building the uterine lining, releasing an egg, and — if there is no pregnancy — shedding that lining.
Typically 24 to 38 days. It is a process, and most of it is invisible.
The period
The bleeding itself. The days you actually bleed — one event that happens inside the cycle, at the end of it.
Typically 8 days or fewer. It is an event, and it is the only part you can see.
So "my cycle is five days" is a description of a period, not a cycle. And "my period is 30 days" is a description of a cycle, not a period. The distinction sounds pedantic until you are trying to tell a clinician what is wrong, at which point the two answers send the consultation in completely different directions.
Why the difference matters: everything runs through ovulation
Here is the physiology in one paragraph. Each cycle, estrogen from a developing ovarian follicle thickens the endometrium — the lining of the uterus. Ovulation releases the egg, and the structure left behind, the corpus luteum, produces progesterone, which matures the lining and holds it in place ready for implantation. If nothing implants, the corpus luteum stops working, progesterone falls, the lining can no longer be maintained, and it sheds. That shedding is the period.
Read that again for what it actually says, because it is the most important sentence on this site:
A menstrual period is progesterone withdrawal bleeding. Progesterone comes only from the corpus luteum. The corpus luteum exists only after ovulation. So a true period only ever happens about two weeks after an ovulation — no ovulation, no period.
That is not a technicality. It means the bleeding is not the event; the bleeding is the receipt for an event that happened a fortnight earlier. And it means bleeding that was not preceded by an ovulation is not menstruation at all — it is estrogen breakthrough or estrogen withdrawal bleeding, which looks similar from the outside and is a different thing underneath.
Three consequences follow, and between them they explain most of what people find confusing:
A period is the end of a cycle, not the beginning of one. We number cycle days from the first day of bleeding purely because it is the one event you can date reliably. Physiologically the bleeding is the last act, not the first.
When ovulation is irregular, bleeding is irregular. When ovulation does not happen at all, there is no progesterone, so the lining keeps thickening under estrogen alone until it breaks down unpredictably — which is why anovulatory bleeding can be both erratic and very heavy, and why prolonged anovulation carries a risk of endometrial hyperplasia. This one mechanism accounts for a large share of unpredictable bleeding in adolescence, in perimenopause, in PCOS and in thyroid disease.
So a problem with your period is usually a symptom, and the actual disorder is one of ovulation. That is why this site keeps returning to it.
The two halves of the cycle
The first half — from the start of bleeding until ovulation — is the follicular phase. Its length varies considerably, both between people and from month to month in the same person. The second half — ovulation to the next period — is the luteal phase, and it is far more consistent, typically around two weeks.
That asymmetry is the practical point. When a cycle runs long or short, it is nearly always the first half moving. Which is why "day 14 is ovulation" holds only for a textbook 28-day cycle, and why counting backwards from the next expected period estimates ovulation better than counting forwards from the last one.
Every abnormality, properly named. Period problems and cycle problems have specific medical names, and the terminology was substantially revised in 2011 and 2018 — so much of the older vocabulary you may have been given is no longer standard. The full reference page defines every term, in plain language or clinical terminology, and says which findings need evaluation rather than reassurance.
Reference ranges
What counts as normal
The international standard is FIGO System 1, which describes menstrual bleeding along four separate axes rather than as one global impression. These are the numbers clinicians use.
| Axis | Normal | Outside normal |
|---|---|---|
| Frequency | Every 24–38 days | Under 24 days = frequent · Over 38 days = infrequent |
| Duration | 8 days or fewer | Over 8 days = prolonged |
| Regularity shortest to longest cycle over a year | Ages 26–41: varies by 7 days or less Ages 18–25 or 42–45: varies by 9 days or less | Greater variation = irregular |
| Volume | Not excessive by the patient's own judgment | Heavy, or light, as reported |
Source: Munro MG, Critchley HOD, Fraser IS; FIGO Menstrual Disorders Committee. Int J Gynaecol Obstet. 2018;143(3):393–408. Confirmed in Jain V, Munro MG, Critchley HOD. Int J Gynecol Obstet. 2023;162(Suppl 2):29–42.
Note what is not in that table. Nothing requires a cycle to be 28 days. In a digital cohort of more than 600,000 cycles the average was about 29.3 days, with wide spread around it. A 33-day cycle that arrives reliably is normal. A 28-day cycle that swings to 40 and back is not.
The cycle is also treated as a vital sign — a readout of endocrine and general health alongside pulse and blood pressure. Cycles that go missing, or that change character and stay changed, are information about the body as a whole, not only about the uterus.
Age changes the answer. Cycles are most variable in the first years after menarche and again in the years before menopause. In between, they are at their most consistent. Any assessment that ignores age will mislabel a normal adolescent and a normal 45-year-old as abnormal.
One mechanism
The same rule explains every state
Once you hold on to the idea that a period is progesterone withdrawal following an ovulation, the whole menstrual life stops being a list of separate topics and becomes one mechanism seen from different angles. Pregnancy, the pill, PCOS, adolescence, perimenopause and menopause are not unrelated chapters. They are all answers to a single question: did an ovulation happen, and what happened to the progesterone afterwards?
| Situation | Ovulation | Progesterone | What the bleeding is |
|---|---|---|---|
| Ordinary ovulatory cycle | Yes | Rises after ovulation, then falls | A true period — progesterone withdrawal bleeding, about two weeks after ovulation. |
| First years after menarche | Often not | Absent in those cycles | Frequently not a true period but estrogen breakthrough or withdrawal bleeding. This is why early cycles are long and unpredictable. |
| Anovulation — PCOS, thyroid disease, hypothalamic causes | No | Absent | Unopposed estrogen builds the lining until it outgrows its support and breaks down. Erratic, sometimes very heavy, and over time a hyperplasia risk. |
| Pregnancy | Yes — followed by implantation | Sustained, first by the rescued corpus luteum and later by the placenta | No withdrawal, therefore no bleeding. The missed period is the mechanism, not merely a sign of it. |
| Combined hormonal contraception — pill, patch, ring | Suppressed | Exogenous progestogen, stopped deliberately in the hormone-free interval | A withdrawal bleed from a drug being paused. Not a period. Skipping it is not "holding a period in". |
| Progestogen-only methods — implant, injection, hormonal IUD | Variably suppressed | Continuous, without cyclical withdrawal | A thin, inactive lining. Unscheduled spotting early on, and often no bleeding at all later. Absence here is expected, not alarming. |
| Lactation | Suppressed | Absent | No bleeding, for as long as suppression lasts. Ovulation returns before the first bleed, which is why the first postpartum ovulation can be missed entirely. |
| Perimenopause | Erratic — some cycles yes, some no | Present in some cycles, absent in others | An unpredictable mixture of true periods and anovulatory bleeding. Exactly the pattern the erratic ovulation predicts. |
| Menopause | Ended | Absent | No bleeding, permanently. Which is precisely why any bleeding after menopause is abnormal and always investigated. |
Mechanisms per standard reproductive physiology; anovulatory bleeding classified as estrogen withdrawal or estrogen breakthrough bleeding. See the references page.
Two things this immediately settles.
The bleed on the pill is not a period. The seven-day hormone-free interval was designed in the 1950s to mimic a natural cycle for cultural and reassurance reasons, not because a monthly bleed was medically necessary. Continuous regimens that skip it are not suppressing something the body needs to do.
And a "late period" is usually a late ovulation. Since the interval from ovulation to bleeding is fairly fixed at around two weeks, while the interval from bleeding to ovulation varies a great deal, a period that arrives late almost always means the ovulation arrived late. The bleeding is not what shifted.
The first period
Menarche
The first period is the one everyone remembers and almost nobody was properly prepared for. It is also the single most misunderstood point on the whole arc, because it looks like a beginning and is actually a midpoint — puberty has been underway for years by the time it arrives.
Breast budding first
Thelarche, not bleeding, is the true start of puberty. The first period typically follows two to three years later.
Menarche
Median age between 12 and 13 years in well-nourished populations. By 15, 98% have started.
The first two years
Cycles are long and irregular because many are anovulatory. This is normal maturation, not a disorder.
Settling
By the third year after menarche, 60 to 80% of cycles run 21 to 34 days — the adult pattern.
The other thing worth knowing is that the first period is not the start of ovulation. Many early cycles are anovulatory, so much early bleeding is not true menstruation at all. Ovulation establishes over the following months to years — and it can also arrive before the first bleed, which is why pregnancy is possible in someone who has never had a period.
The first bleed itself usually lasts two to seven days. Cycles in the first year average around 32 days, and 90% fall between 21 and 45 days — a much wider window than the adult 24 to 38. Applying adult reference ranges to a 13-year-old will label normal maturation as pathology, which is why the age-specific thresholds exist.
What still needs looking at, even in the first years. No period by age 15, or more than three years after breast development began. No breast development by 13. A gap of 90 days or more between periods, even once. Bleeding longer than seven days, or soaking through a pad or tampon every one to two hours. And heavy bleeding from the very first period, which is the classic presentation of an undiagnosed bleeding disorder — the one thing at this age that most often gets dismissed as ordinary.
The age is falling, and the guidance has not caught up. ACOG describes the median age at menarche as having remained relatively stable between 12 and 13 years. A 2024 analysis of 71,341 US participants found mean age fell from 12.5 years in those born 1950–1969 to 11.9 years in those born 2000–2005, with menarche before age 11 rising from 8.6% to 15.5%. Cycles are also taking longer to settle: the proportion reaching regularity within two years fell from 76% to 56%. Both statements are current, they conflict, and this site reports the conflict rather than picking one. The full picture is here.
Heavy menstrual bleeding
Why nobody agrees on what "heavy" means
Three definitions are in current use, and they identify different women. None is wrong; each was built for a different purpose.
| Definition | Threshold | Built for |
|---|---|---|
| Research / volumetric | More than 80 mL of measured blood loss per cycle | Trials and physiology. Not measurable in ordinary life. |
| NICE, adopted by FIGO and ACOG | Blood loss that interferes with physical, emotional, social or material quality of life | Clinical care. Puts the patient's experience at the centre. |
| CDC | Bleeding lasting more than 7 days, or soaking through a pad or tampon more often than every 2 hours | Public health screening. Fast, countable, no judgment call. |
A woman can meet the CDC criteria and fall under 80 mL. She can lose well over 80 mL and say her life is unaffected. Both are common, and neither is an error. Rather than reconciling the three, the blood-loss tool below reports each separately and tells you when they disagree — because the disagreement is itself clinically useful.
The measurement problem nobody mentions
Estimating volume from products only works if the product reached the end of its useful life at the moment it was changed. Changed on a schedule and not full, the estimate runs high. Already at capacity or leaking before the change, the estimate runs low — and the interval it took to fill reveals the peak flow rate, which often matters more than the daily total. The tool asks about this directly instead of assuming.
The second complication is modern products. Cups, discs and period underwear hold far more than pads and tampons, and marketed capacity is not interchangeable with red-blood-cell volume. Published capacity measurements, not label claims, are what the tool uses.
Tools · cycles and bleeding
Check your own cycle
Which one do I want? Use Cycle Length & Regularity if you have your period start dates and want them scored precisely. Use Is My Cycle Normal? if you do not have dates and want to work through symptoms in plain language. Use Period Pain Navigator if the problem is pain rather than the bleeding — including when the bleeding itself is entirely normal.
The last period
Perimenopause and menopause
The mechanism above is the whole of it: the ovaries stop ovulating, so there is no corpus luteum, no progesterone, and therefore nothing to withdraw. Menstruation ends because ovulation ends. Everything else about the transition follows from ovulation becoming erratic on its way to stopping.
Menopause is a single day, and it can only be identified in hindsight: the day twelve consecutive months have passed since the final menstrual period. Everything people describe as "going through menopause" is actually perimenopause — the transition leading up to it, which commonly runs for years and produces the symptoms.
The transition is staged formally using STRAW+10, which anchors each stage to changes in cycle pattern rather than to symptoms or to a blood test. That matters, because it means your cycle history is the diagnostic instrument. A single FSH level in a woman still having periods tells you very little; FSH fluctuates widely across the transition, and a normal value does not exclude it.
Late reproductive
Cycles still regular, but subtly shorter. Fertility is already declining before anything looks different.
Early transition
A persistent difference of 7 days or more between consecutive cycles. This is the entry point to perimenopause.
Late transition
An interval of 60 days or more without a period. Hot flashes are most likely in this window.
Postmenopause
Begins 12 months after the final period. Symptoms may continue for years afterwards.
Framework: Stages of Reproductive Aging Workshop +10 (STRAW+10), applied by the Perimenopause Stage Finder below.
What changes, beyond hot flashes
Vasomotor symptoms get the attention, but the transition also affects sleep, mood, cognition, bone density, lipids, blood pressure, body composition and genitourinary tissue. Genitourinary syndrome of menopause differs from the rest in one important respect: it does not improve on its own with time. It progresses. Treating it early is easier than treating it late.
Bleeding changes during perimenopause are expected — but not all of them are benign. Bleeding that is very heavy, that occurs between periods, or that occurs at any point after menopause has been reached needs evaluation, not reassurance.
Major development · 2025–2026
The FDA removed the boxed warnings from menopausal hormone therapy
On 10 November 2025 the FDA and HHS announced they would initiate removal of the broad boxed "black box" warnings from hormone therapy products for menopause. On 12 February 2026 the FDA approved the first batch of six revised labels, removing the risk statements for cardiovascular disease, breast cancer and probable dementia. Twenty-nine manufacturers had submitted proposed label changes by that date.
What did not change: the boxed warning for endometrial cancer on systemic estrogen-alone products in women with a uterus remains. Progestogen is still required to protect the endometrium.
What it means, and what it does not. Those warnings came from the 2002 Women's Health Initiative results — a trial whose participants averaged 63 years of age, more than a decade past menopause, using a formulation that is no longer standard. Applying that finding to a symptomatic 51-year-old was always a misreading, and it left two decades of women undertreated. Correcting the label corrects the misreading. It does not make hormone therapy right for everyone, it does not abolish individual contraindications, and it does not turn a symptom treatment into an anti-ageing intervention. The decision remains individual, and it still belongs in a conversation with your own clinician.
Sources: FDA/HHS news release, 10 November 2025; FDA news release, 12 February 2026. Full citations on the references page.
Tools · the transition
Find out where you are
About
What this site is, and is not
Menstria is a set of structured ways to organise what you already know about your own body against published criteria. It does not diagnose anything. Bleeding that is heavy, prolonged, irregular or newly changed has many possible causes — structural, hormonal, haematological and systemic — and separating them requires examination and testing. Bring the output to a clinician; do not use it instead of one.
Every calculation runs in your browser. Nothing you type is transmitted, logged or stored.
Where the evidence is genuinely uncertain, these tools say so and show the range rather than inventing a precise-looking number. Where major frameworks disagree, they show the disagreement. Every figure traces to a specific publication, listed in full on the references page.
Built by Amos Grünebaum, MD — Professor of Obstetrics & Gynecology and Maternal-Fetal Medicine. Part of ObGyn Intelligence.