The four phases of the menstrual cycle

What your body is doing in each phase, which hormones lead, how long each one usually lasts, and why your cycle may not match the diagram.

Last reviewed 19 October 2026Checked against the sources listed below

This guide is for anyone who has heard about “cycle phases” and wants to know what is actually going on in each one: what your ovaries and uterus are doing, which hormones lead, how long each phase usually lasts, and why your own cycle may not match the version in a diagram.

The four phases at a glance

A cycle is counted from the first day of one period to the first day of the next.^[1] Inside it, four phases follow each other in the same order every time:

One detail trips people up. In the medical definition, the follicular phase begins on the first day of your period and lasts until ovulation, so it overlaps with your period.^[6] The four-phase version that most apps use, Bloom included, gives the days you bleed a name of their own and starts the follicular phase when your period ends. Both describe the same cycle; they just draw the first line in a different place.

To see how each hormone rises and falls across the whole cycle, see the menstrual cycle hormone chart.

1. The menstrual phase

Day one of your period is day one of your cycle. Your period comes because no pregnancy started in the cycle before: estrogen and progesterone fall, and the lining that built up in the uterus is shed.^[2] Bleeding for anything from three to seven days is normal, according to Cleveland Clinic.^[2]

How these days feel is personal. Some people barely notice them and others plan around them. A few cycles of notes about your energy, pain and mood during your period will tell you more about your own pattern than any general description can.

2. The follicular phase

While you are still bleeding, the next cycle is already under way. Follicle-stimulating hormone (FSH) makes follicles in an ovary grow, and rising estrogen rebuilds and thickens the lining of the uterus.^[2] The phase lasts as long as it takes one dominant follicle to bring an egg to maturity.^[6]

This is the part of the cycle that stretches and shrinks. Researchers who analysed more than 600,000 cycles logged in the Natural Cycles app found that the follicular phase lasted 16.9 days on average, with most between 10 and 30 days, and that it shortened by about 0.19 days for each year of age between 25 and 45.^[3] So a longer or shorter cycle usually means a longer or shorter follicular phase, because the luteal phase varies much less.^[3] The follicular phase guide goes into this phase in more detail, including energy.

3. Ovulation

At the end of the follicular phase, a surge of luteinizing hormone (LH) causes the ovary to release the mature egg.^[4] Once released, the egg survives for about 12 to 24 hours unless it is fertilized.^[4] Ovulation is the only phase that is really a single event rather than a run of days, and it is also the one you can’t see happen.

You will often read that ovulation falls on day 14, and in a 28-day cycle that is roughly where it lands.^[2] In a longer cycle it usually comes later, since most of the extra days sit in the follicular phase.^[3] That is a description of how the cycle works, not a way to find your fertile days: a phase guide, or a phase in an app, is not contraception and not a method for planning a pregnancy.

4. The luteal phase

After the egg is released, the follicle it came from turns into the corpus luteum, which makes progesterone along with some estrogen.^[5] Progesterone is the hormone that thickens the lining of the uterus in this phase, getting it ready in case a pregnancy begins.^[5]

The luteal phase is the steadier half of the cycle. It usually lasts 12 to 14 days, and 10 to 17 days is considered normal, according to Cleveland Clinic.^[5] If no pregnancy begins, estrogen and progesterone fall, the lining is shed, and your next period starts a new cycle.^[2]

The days before a period are also when premenstrual symptoms show up, and changes in mood, appetite or sleep are among the common ones.^[7] Noting when they start and stop for a few cycles makes it easier to tell whether they follow your cycle or something else. There is more on this phase, including cravings and what a short luteal phase means, in the luteal phase guide.

Why your cycle may not match the diagram

Diagrams of the four phases are nearly always drawn for a 28-day cycle. That is a convenient example, not a target: the U.S. Office on Women’s Health counts cycles from 24 to 38 days as normal.^[1] If your cycle is 33 days, your phases aren’t running late; your follicular phase is probably just longer than the one in the picture.

The lines between phases are also softer than a chart makes them look: a chart has to put each boundary on a single day, so “day 1 of the luteal phase” is a line drawn for convenience. And not every cycle includes ovulation: irregular cycles can be ovulatory or anovulatory.^[8]

How Bloom uses the four phases

Bloom reads your month as these four phases. Your menstrual phase comes straight from the period you log, so it is never a guess. The other three are estimates built from your history: Bloom places ovulation by counting back from your next expected period, which means a longer cycle gets a longer follicular phase instead of an ovulation day fixed at 14. The cycle phase tracker page explains exactly how it decides which phase you are in today.

For each phase, Bloom shows a chart of how estrogen, progesterone and testosterone typically move, lets you set one focus for the phase, and compares your check-ins with what the phase usually brings. The charts are educational curves, not your own levels.

What Bloom can’t do matters just as much. It can’t confirm that you ovulated or measure your hormones, and it is not a fertility tool or contraception. If you want to plan your weeks around your phases, the cycle syncing page covers how that works and what the evidence does and doesn’t show.

Making the phases useful

• Start from day one. Log the first day of every period; it anchors every phase that follows.
• Learn your own lengths. After a few cycles, note how long your period and your whole cycle usually last. Those two numbers tell you more than any diagram.
• Look for patterns, not labels. Log energy, mood and sleep for a few cycles and see whether they really follow your phases. For some people they do; for others the pattern is weak.
• Check what counts as normal. If your cycle seems long or short, see is my cycle length normal? for the ranges health bodies use.

Bloom is a wellness and planning app. It is not a medical device, it does not diagnose or treat any condition, and it is not a method of contraception. This page is general information, not medical advice. If something about your cycle worries you, talk to a doctor, nurse or midwife.