The menstrual cycle phases explained, one at a time
The menstrual cycle phases explained: what happens hormonally in the menstrual, follicular, ovulatory, and luteal phases, plus their rough timing.
The menstrual cycle moves through four phases: the menstrual phase, the follicular phase, the ovulatory phase, and the luteal phase. Each is driven by hormones rising and falling in sequence, and together they run from the first day of one period to the first day of the next. The short version: your period, the build-up to releasing an egg, the release itself, and the wait for the next period.
This is a plain-language tour of what happens in each phase and why the timing matters. It is general education about how the cycle works, not medical advice, and it cannot tell you anything specific about your own body.
The four phases at a glance
On a roughly 28-day cycle, the phases line up something like this. Treat the day numbers as a rough map, not a rule, because real timing varies a great deal.
| Phase | Rough timing | What is happening |
|---|---|---|
| Menstrual | Days 1 to about 5 | The uterine lining sheds as your period |
| Follicular | Day 1 until ovulation | An egg matures and estrogen climbs |
| Ovulatory | Around the middle | A mature egg is released |
| Luteal | Ovulation to next period | The body prepares for a possible pregnancy |
The menstrual and follicular phases overlap, because your period happens during the early follicular phase. The four names describe what is going on hormonally, not four tidy boxes with hard walls between them.
The menstrual phase
The menstrual phase is your period, and it is counted as day one of the whole cycle. It begins when hormone levels from the previous cycle drop, which signals the uterine lining to shed. That shedding is the bleeding you see.
Bleeding commonly lasts somewhere between 2 and 7 days, with the heaviest flow usually in the first few days. Cramps, tiredness, and lower energy are common in this stretch. Because day one is the anchor for every cycle calculation, it is the single most useful thing to record.
The follicular phase
The follicular phase starts on the same day your period does and runs until ovulation, so it overlaps the back end of your bleeding. Its job is to ripen an egg.
A hormone from the brain prompts several follicles in the ovaries to develop, and usually one becomes dominant. As that follicle grows, it produces rising estrogen, which rebuilds the uterine lining and, near the end, triggers the surge that leads to ovulation. This is the phase where energy often picks back up.
The follicular phase is also the flexible one. It can be longer or shorter depending on how long the egg takes to mature, which is the main reason two people can both be perfectly normal with very different cycle lengths. Where those usual ranges sit is covered in how long is a normal menstrual cycle.
The ovulatory phase
Ovulation is the release of the mature egg from the ovary, prompted by a sharp rise in a hormone called LH (the LH surge). The egg then travels into the fallopian tube, where it can be fertilized for a short window of roughly a day.
Because sperm can survive for several days, the fertile window is usually counted as the few days leading up to ovulation plus ovulation day itself, not just the single day of release. If you are tracking for pregnancy, the ovulation calculator estimates this window from your cycle dates. For a deeper walk-through of the signs, the fertile window guide goes further than we do here.
The luteal phase
After the egg is released, the empty follicle transforms into a structure called the corpus luteum, which produces progesterone. Progesterone keeps the uterine lining thick and ready in case a fertilized egg implants.
If pregnancy does not occur, the corpus luteum winds down, progesterone falls, and that drop triggers the next period, which starts the whole cycle again. The premenstrual stretch, with its familiar bloating, mood shifts, tender breasts, or changes in sleep, lives in the late luteal phase as hormones fall.
Why the luteal phase is steadier than the follicular phase
Here is the part that makes period prediction possible. The luteal phase tends to be relatively consistent in length, often close to two weeks, because the corpus luteum has a fairly fixed lifespan once ovulation has happened. The follicular phase is the variable one, since it stretches or shrinks with how long the egg takes to mature.
The practical consequence: most of the month-to-month change in your total cycle length comes from the follicular half, while the back half stays roughly the same. That is why ovulation is usually estimated by counting back about 14 days from the next expected period rather than forward from the last one. If you know your average cycle length, you can estimate both your next period and your ovulation, and the free period calculator does that arithmetic for you. The reasoning behind that count-back is covered in how to predict your next period.
Seeing your own phases
Reading about the phases is one thing; watching them line up with how you actually feel is another. A tracker that colors your calendar by phase makes the pattern visible, so a low-energy day or a wave of cramps sits next to the phase it belongs to.
PeriodOS does this as a single offline HTML file. It draws a three-month calendar shaded by phase, estimates your next period, ovulation, and fertile window, and lets you log flow, symptoms, and mood day by day. Everything stays in your browser on your own device, with no account and nothing uploaded, which is worth knowing for a record this personal.
Watch one full cycle
The fastest way to make the phases real is to track a single cycle from one period to the next, noting your energy, mood, and symptoms as you go. One loop through all four phases will teach you more about your own pattern than any general timeline can, and it gives you the dates a prediction needs.
This article is general education, not medical advice, and it cannot diagnose anything. Talk to your own doctor or clinician about your cycle and any change that concerns you.
Frequently asked questions
What are the four phases of the menstrual cycle?
The four phases are the menstrual phase (your period), the follicular phase (the run-up to ovulation as an egg matures), the ovulatory phase (the release of the egg), and the luteal phase (the stretch between ovulation and the next period). They are driven by rising and falling hormones and repeat with each cycle.
How long does each menstrual cycle phase last?
On a roughly 28-day cycle, the period lasts about 2 to 7 days, the follicular phase runs from the start of your period until ovulation, ovulation happens around the middle, and the luteal phase fills the roughly two weeks before the next period. Timing varies a lot between people, and most of the difference in total cycle length comes from the follicular phase.
Why is the luteal phase more stable than the follicular phase?
After ovulation the empty follicle becomes a structure called the corpus luteum, which produces progesterone for a fairly consistent stretch of roughly two weeks before it winds down. The follicular phase, by contrast, can be stretched or shortened depending on how long it takes an egg to mature. That is why the luteal phase length tends to be steadier from cycle to cycle.
Which phase am I most likely to get pregnant in?
The fertile window falls in the ovulatory phase and the days just before it, because sperm can survive for several days and the egg is available for about a day after release. This is an estimate, not a guarantee of timing. An ovulation estimate can point you at the window, but it cannot pinpoint the exact day.
Do the phases feel different?
Many people notice shifts in energy, mood, sleep, appetite, and skin across the cycle, and those patterns can be real for you even though they vary widely from person to person. Tracking how you feel alongside your cycle dates is the way to see your own pattern. There is no single correct way the phases are supposed to feel.
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