Menstrual cycle phases: the 4 phases and how long each lasts

A menstrual cycle is counted from the first day of a period to the day before the next one starts (NHS, 2023). Diagrams usually show a 28-day cycle with ovulation on day 14, but measured cycles rarely follow that pattern exactly, and the phases of the menstrual cycle make more sense once you know which of them stretch and which stay steady. The period calculator and the ovulation calculator on this site work from the same phases.

The 4 phases of the menstrual cycle, in order

1. Menstrual phase. The period: the lining of the womb comes away and leaves the body (NHS, 2023).
2. Follicular phase. From the first day of the period to ovulation: follicles in the ovary grow and estrogen rises (NICHD, 2026).
3. Ovulation. An ovary releases an egg, about a day and a half after luteinizing hormone begins to surge (Office on Women's Health, 2025).
4. Luteal phase. From ovulation to the next period: progesterone prepares the lining of the womb for a possible pregnancy (MedlinePlus, "Progesterone Test", 2025).

The menstrual phase and the follicular phase overlap, because both begin on the first day of bleeding. That is why some sources describe the stages of the menstrual cycle as two halves, before and after ovulation, and others as four. This guide uses the four phases of the menstrual cycle that most health sites name, sometimes called the menstrual cycle stages, and gives each one the length that measured cycles show rather than a fixed run of days.

The NHS puts the length of a period at about 2 to 7 days (NHS, 2023), and ACOG counts bleeding that lasts more than 7 days as abnormal (ACOG, 2021). The averages and ranges for the follicular and luteal phases come from 612,613 ovulatory cycles logged by 124,648 users of a fertility app (Bull et al., 2019). Those users estimated ovulation from temperature and urine LH tests, so the figures describe people who track their cycles closely. The egg's lifespan of 12 to 24 hours is from the US Office on Women's Health (Office on Women's Health, 2025), and the range for ovulation comes from a study of 221 women in which it came as early as day 8 and as late as day 60 (Wilcox et al., 2000).

What happens in each phase of the menstrual cycle

Menstrual phase

The menstrual phase is the period itself. If no pregnancy has started, levels of estrogen and progesterone fall, and the lining of the womb comes away and leaves the body as the period (NHS, 2023). The first day of bleeding is day 1 of the cycle. The NHS puts the blood lost in a period at about 20 to 90 ml, roughly 1 to 5 tablespoons (NHS, 2023).

Follicular phase

The follicular phase starts on the first day of the period and ends at ovulation. Follicle-stimulating hormone (FSH) triggers the growth of eggs in the ovaries and gets them ready for ovulation (MedlinePlus, "Follicle-Stimulating Hormone (FSH) Levels Test", 2023). After bleeding ends, usually around day 5, estrogen rises and the lining of the womb thickens, while follicles, the small sacs in the ovary that hold the eggs, grow and mature until one is ready to release its egg (NICHD, 2026). It is the phase whose length varies most from one cycle to the next (Fehring et al., 2006).

Ovulation phase

Ovulation is the release of an egg from an ovary, and luteinizing hormone (LH), made by the pituitary gland at the base of the brain, triggers it (MedlinePlus, "Luteinizing Hormone (LH) Levels Test", 2023). LH begins to surge about 36 hours before ovulation and peaks about 12 hours before it (Office on Women's Health, 2025). In an average 28-day cycle the egg is released around day 12 to 14, but ovulation can come anywhere between day 10 and day 21 (NICHD, 2026). The ovulation phase is when signs such as clearer, more slippery mucus and cramping on one side can appear (Office on Women's Health, 2025). The guide to ovulation symptoms sets out which signs come before ovulation and which come after it.

Luteal phase

The luteal phase runs from ovulation to the day before the next period. After the egg is released, progesterone levels rise and prepare the lining of the womb for a fertilized egg to attach (MedlinePlus, "Progesterone Test", 2025). If no pregnancy starts, estrogen and progesterone fall and the period begins (NHS, 2023). The NHS puts the time from the release of an egg to the start of a period at around 10 to 16 days (NHS, 2023).

Menstrual cycle hormones across the phases

Four hormones run the cycle, and the changes in hormones during the menstrual cycle are what move it from one phase to the next. Two come from the pituitary gland and act on the ovaries; two come from the ovaries and act on the lining of the womb. The table is a menstrual cycle hormone chart in words: it shows which hormone leads in each phase rather than measured levels, which differ from person to person.

FSH and LH are both made by the pituitary gland, and the hormones the ovaries make tell the brain when to start and stop making them (MedlinePlus, "Follicle-Stimulating Hormone (FSH) Levels Test", 2023; MedlinePlus, "Luteinizing Hormone (LH) Levels Test", 2023). Progesterone is made mainly by the ovaries: in the first half of the cycle estrogen makes the lining of the womb thicker, and in the second half progesterone rises (MedlinePlus, "Progesterone Test", 2025). Very low levels of estrogen and progesterone at the end of a cycle without pregnancy are the signal for the period to begin (Office on Women's Health, 2025).

Drawn as lines, the same chart shows estrogen climbing before ovulation, a short, steep spike of LH, and progesterone rising after ovulation and falling before the period. Exact levels differ between people and between cycles, which is one reason a blood test for FSH may need to be done on a particular day of the cycle (MedlinePlus, "Follicle-Stimulating Hormone (FSH) Levels Test", 2023).

Menstrual cycle phases and symptoms

The changing levels of estrogen and progesterone through the cycle can cause menstrual symptoms (Office on Women's Health, 2025). The pattern that medical sources describe best is premenstrual syndrome (PMS). Its symptoms start in the second half of the cycle, 14 or more days after the first day of the last period, and usually go 1 to 2 days after the next period starts (MedlinePlus, 2026). The most common include:

• bloating or feeling gassy
• breast tenderness
• constipation or diarrhea
• food cravings
• headache
• clumsiness, and less tolerance for noise and light

MedlinePlus also lists changes in mood among PMS symptoms, including mood swings, tension or anxiety, sadness, irritability and sleep problems (MedlinePlus, 2026). Beyond PMS, the evidence linking the 4 phases of the menstrual cycle and moods is limited. MedlinePlus states that the exact cause of PMS is not known and that a role for changing brain hormone levels has not been proven (MedlinePlus, 2026). Claims that each phase has its own personality, or that food and exercise should be matched to the phase, are not supported by the sources cited here. A symptom diary kept for at least 3 months shows whether symptoms follow the cycle (MedlinePlus, 2026).

Some people also notice signs around ovulation itself: minor cramping on one side of the pelvis, and mucus that becomes more slippery and clear (Office on Women's Health, 2025). The guide to ovulation pain covers the cramping.

Luteal vs follicular phase

ACOG describes the days between ovulation and the next period as the most consistent part of the menstrual cycle (ACOG, 2019), and a study of 1,060 cycles from 141 women found that the follicular phase contributed most of the variation in cycle length (Fehring et al., 2006). The app data agree: from age 25 to 45, the average follicular phase shortened by 0.19 days a year, almost exactly matching the 0.18 days a year by which the whole cycle shortened (Bull et al., 2019). In practice, a cycle that runs long usually means ovulation came late, not that the luteal phase stretched.

How long is a normal menstrual cycle?

The NHS gives the average as about 28 days and says regular cycles from 21 to 35 days are normal (NHS, 2023). ACOG gives the same normal menstrual cycle length, typically between 21 and 35 days (ACOG, 2021). The US Office on Women's Health uses a wider range and calls periods regular if they usually come every 24 to 38 days (Office on Women's Health, 2025). The two ranges overlap but do not match, so a 22-day or a 37-day cycle counts as normal by one and falls outside the other. In teenagers, NICHD notes that the cycle can range from 21 to 45 days (NICHD, 2026).

Measured cycles are rarely exactly 28 days. In the app data the average menstrual cycle length was 29.3 days, and only 13 in 100 cycles were 28 days long (Bull et al., 2019). In the study of 141 women, 95 in 100 cycles lasted 22 to 36 days, and 42.5 in 100 women had cycles that varied by more than 7 days (Fehring et al., 2006). Even in cycles of exactly 28 days, ovulation fell 14 days before the next period in only about 1 in 10, and only about 30 in 100 women had their whole fertile window within days 10 to 17 (Wilcox et al., 2000).

How to track your menstrual cycle

The simplest record is a calendar: mark the first day of each period, and after a few months it shows whether your periods are regular. The US Office on Women's Health suggests noting when bleeding starts, how heavy it is on the heaviest days, how many days it lasts and any symptoms, and says apps can hold the same record (Office on Women's Health, 2025). The NHS suggests an app or a diary (NHS, 2026). The period calculator turns the date your last period started and your usual cycle length into predicted dates, and the ovulation calculator estimates your fertile days from the same two numbers.

A calendar shows the cycle after the fact. Three body signs track the phases as they happen: cervical mucus becomes thin and slippery just before ovulation, an LH surge shows on a urine test, and basal body temperature rises around ovulation and stays higher until the end of the cycle (ACOG, 2019; Office on Women's Health, 2025). The guides to cervical mucus, ovulation predictor kits and basal body temperature cover each one, and the guide to the most fertile days shows where the fertile window falls.

When to see a doctor about your cycle

ACOG lists the cycle patterns that count as abnormal and are worth raising with a doctor (ACOG, 2021):

• cycles shorter than 21 days or longer than 35 days
• cycle length that varies by more than 7 to 9 days
• no period for 3 to 6 months
• bleeding that lasts more than 7 days
• bleeding or spotting between periods or after sex

The US Office on Women's Health advises talking to a doctor or nurse about cycles longer than 38 days or shorter than 24 days, and about going 90 days without a period when you are not pregnant or breastfeeding (Office on Women's Health, 2025). ACOG adds that periods are often somewhat irregular in the first years after they start and around age 50 (ACOG, 2021). The guide to irregular periods covers the causes and what a doctor may check.