--- title: "Menstrual cycle phases: the four stages of your month, explained" description: "The four menstrual cycle phases explained: what happens in your period, the follicular phase, ovulation and the luteal phase, and when to see a doctor." canonical: https://www.sisly.ai/en/blog/menstrual-cycle-phases/ published: 2026-09-30 updated: 2026-09-30 language: en --- # Menstrual cycle phases: the four stages of your month, explained There are four menstrual cycle phases: menstruation (your period), the follicular phase, ovulation and the luteal phase. A cycle runs from the first day of one period to the day before the next, and usually lasts 21 to 35 days. Hormones rise and fall across it, and temperature, energy and mood can shift with them. - The cycle has four phases: menstruation, the follicular phase, ovulation and the luteal phase. - Most cycles last 21 to 35 days, and a period usually lasts 2 to 7 days, according to the NHS. - The follicular phase is the part that varies most; the luteal phase usually lasts 10 to 17 days. - Ovulation does not always fall on day 14, even in regular cycles. - Your own pattern over several months tells you more than any textbook average. ## What are the four menstrual cycle phases? The menstrual cycle is the monthly rhythm through which the body prepares for a possible pregnancy. It runs from the first day of one period to the day before the next. Across it, a small set of hormones rises and falls in a regular order, and each step has a name. The four menstrual cycle phases are: 1. **Menstruation**, or the menstrual phase: your period, when the lining of the womb is shed. 2. **The follicular phase**: from the first day of your period until ovulation, while an egg matures in one of the ovaries. 3. **Ovulation**: the release of that egg from the ovary. 4. **The luteal phase**: from ovulation until the next period, when the body holds the lining of the womb ready in case of pregnancy. The first two overlap: the follicular phase begins on the first day of your period, so the days of bleeding sit inside it. That is why the cycle is sometimes described as two halves, the follicular half before ovulation and the luteal half after it. | Phase | When, in a 28-day cycle | Main hormones | What you may notice | |---|---|---|---| | Menstruation | Days 1 to about 5 | Oestrogen and progesterone at their lowest | Bleeding, cramps, tiredness | | Follicular phase | Day 1 until ovulation | FSH, then rising oestrogen | For some, mood lifts towards ovulation | | Ovulation | Around day 14 | A surge of LH | Clear, slippery discharge; for some, a one-sided twinge | | Luteal phase | About day 15 to day 28 | Progesterone, with some oestrogen | Slightly higher temperature; bloating, tender breasts or mood changes before the period | A 28-day cycle is a teaching example, not a rule; the days in the table move with your own cycle length. ## Why does understanding your cycle matter? Periods are often a private subject, shared with a mother, a sister or a doctor. That privacy deserves respect. Knowing how the cycle works still helps, because it turns changes that seem random into a pattern you can recognise. The World Health Organization made the same point in its 2022 statement on menstrual health and rights. It asked that menstruation be recognised as a health issue, not a hygiene issue, with physical, psychological and social dimensions, and that it be considered across the whole of life, from before the first period to after the menopause. Knowing your phases explains why some weeks feel different from others, gives you words and dates to bring to a doctor, and puts other readings in context, such as a slightly higher resting temperature in the second half of the month. ## How long is a normal menstrual cycle? The NHS says that for most women a period comes around every 28 days, and that anything from every 21 to every 35 days is common. Cleveland Clinic gives the same range and describes an average of 28 days. A 2019 study in npj Digital Medicine looked at 612,613 cycles recorded by 124,648 users of a cycle-tracking app. The average cycle lasted 29.3 days. The same study found that cycles shortened slightly with age, by about 0.18 days for each year between the ages of 25 and 45. Cycle length changes across life: - **The first years.** The NHS says periods usually begin at around 12, and most women settle into a regular pattern by 16 to 18. - **The years before the menopause.** The NHS says the perimenopause, the time when periods start to change before they stop, usually begins between 45 and 55. In the UK, the average age of the menopause is 51. A cycle that varies by a few days is common. Cycles that become irregular for several months, or periods that stop, are a reason to see a doctor. ## What happens during your period? Menstruation is the first phase. If no pregnancy began in the previous cycle, the levels of oestrogen and progesterone fall. The lining of the womb, called the endometrium, is no longer needed and is shed through the vagina as your period. The NHS says a period can last between 2 and 7 days, and usually lasts about 5. Over those days most women lose about 20 to 90 ml of blood, which is about 1 to 5 tablespoons, although some bleed more heavily than this. ### Why do periods hurt? Period pain is common. ACOG, the American College of Obstetricians and Gynecologists, explains that cramps before and during a period are caused by natural chemicals called prostaglandins, made in the lining of the womb. They make the muscles of the womb contract. Their level is highest on the first day of a period, which is why the first day or two are often the most uncomfortable. The NHS says period pain usually lasts up to 3 days. It lists warmth on the tummy from a heat pad or a hot water bottle wrapped in a towel, a warm bath or shower, gentle exercise such as walking, swimming or yoga, and over-the-counter painkillers such as paracetamol or ibuprofen as things that can help. ACOG notes that anti-inflammatory painkillers such as ibuprofen are not suitable for everyone, including people with asthma, stomach ulcers or bleeding disorders, so a pharmacist or doctor is the person to ask. ### How heavy is too heavy? Bleeding varies between women, but some signs suggest a period is heavier than it should be. The NHS lists needing to change a pad or tampon every 1 to 2 hours, needing two kinds of product at once, periods lasting more than 7 days, clots larger than about 2.5 cm, bleeding through to clothes or bedding, and feeling tired or short of breath a lot. ACOG adds needing to change pads during the night. ACOG describes heavy menstrual bleeding as very common, with about one in three women seeking treatment for it. It is treatable, so it is worth raising with a doctor rather than putting up with it. ## What happens in the follicular phase? The follicular phase starts on the first day of your period and ends at ovulation. It is named after the follicles, the tiny fluid-filled sacs in the ovaries that each hold an immature egg. Early in this phase, follicle-stimulating hormone (FSH) signals the ovaries to start growing several follicles. Cleveland Clinic describes how one of them grows faster than the others and becomes the dominant follicle, and the egg inside it matures. During this phase the level of oestrogen rises. Oestrogen rebuilds and thickens the lining of the womb after the period, ready in case a fertilised egg needs somewhere to implant. In the 2024 ring study described further down, mood was most positive around ovulation, though this varies from woman to woman. The follicular phase is the part of the cycle that varies most. Cleveland Clinic says it usually lasts 14 to 21 days and can change from one cycle to the next. In the 2019 study of more than 600,000 cycles, it averaged 16.9 days and ranged widely, from about 10 to 30 days. So when a cycle runs long, the extra days usually come before ovulation rather than after it. ## What happens at ovulation? Ovulation is the moment an ovary releases a mature egg. Cleveland Clinic explains that a sudden rise in luteinising hormone (LH) causes the ovary to release the egg from the dominant follicle. Cleveland Clinic says the egg survives about 12 to 24 hours after it is released. If it is not fertilised, it breaks down and the body reabsorbs it. ### When does ovulation happen? Day 14 is the figure most people know, but it only describes a 28-day cycle. The NHS says ovulation happens about 12 to 16 days before the start of your next period. In a 35-day cycle, that puts it closer to day 21. In a 24-day cycle, closer to day 10. The day can also move from month to month. A 2000 study in the BMJ tracked ovulation with hormone tests in 696 cycles from 221 women. It found that the timing varied widely, even in women whose cycles were usually regular, and that only about 30% of the women had their fertile days entirely within the days 10 to 17 that clinical guidance then assumed. ### What are the signs of ovulation? Cleveland Clinic describes several signs. Not every woman notices them, and none of them is precise on its own. - **Discharge.** In the days just before ovulation, cervical mucus often becomes clear and slippery. - **A one-sided twinge.** Some women feel a brief cramp or ache low on one side, called mittelschmerz. - **Tender breasts or bloating** around the middle of the cycle. - **A small rise in temperature**, which comes after ovulation rather than before it. Ovulation and a period are separate events. Cleveland Clinic notes that it is possible to bleed without having ovulated in that cycle, and ACOG adds that irregular ovulation is common in the first years after periods start and in the years before the menopause. ## What happens in the luteal phase? The luteal phase begins after ovulation and ends when your next period starts. After the egg is released, the empty follicle changes into a structure called the corpus luteum. The corpus luteum makes progesterone, along with some oestrogen. Progesterone keeps the lining of the womb thick and ready for a possible pregnancy. Cleveland Clinic says it also thickens cervical mucus. If a pregnancy begins, progesterone stays raised. If not, progesterone and oestrogen fall towards the end of the phase, and the lining is shed as the next period. The luteal phase is steadier than the follicular phase. Cleveland Clinic says a luteal phase of 10 to 17 days is usual, with an average of 12 to 14. The 2019 app study found an average of 12.4 days. A luteal phase shorter than 10 days is called a short luteal phase, and it is something a doctor can look into if you are trying to conceive. ### Why do I feel different before my period? Many women notice physical or mood changes in the days before a period. The NHS lists mood swings, tiredness, bloating, tender breasts, headaches and changes to the skin among the most common. ACOG adds food cravings, trouble sleeping or needing more naps, difficulty concentrating, and feeling anxious, irritable or tearful. When these symptoms come back month after month and affect everyday life, ACOG calls them premenstrual syndrome, or PMS. To diagnose PMS, a doctor looks for symptoms in the 5 days before a period, across at least three cycles in a row, that ease within 4 days of the period starting. A more severe form, premenstrual dysphoric disorder (PMDD), affects a small number of women and can seriously disrupt work and relationships. It is a medical condition, and help is available. The NHS suggests a symptom diary for at least two cycles, and ACOG two to three months, with the dates of your periods. A written record makes a conversation with a doctor easier. ## How do your temperature, heart rate and sleep change across the cycle? **Temperature.** Basal body temperature is your temperature at complete rest. Cleveland Clinic says it rises by about 0.4 to 1°F after ovulation, roughly 0.2 to 0.6°C, and usually drops again before your period. Progesterone is the reason. The change is small, and Cleveland Clinic lists alcohol, fever, short sleep, stress, some medicines and travel across time zones among the things that can move it. Our guide to [your cycle and your own temperature](https://www.sisly.ai/en/blog/your-cycle-from-your-temperature/) explains how skin temperature measured at night follows a similar pattern. **Heart rate.** A 2024 study in the Journal of Biological Rhythms followed 116 women aged 18 to 55 through one cycle, wearing a ring. Among the 96 whose temperature showed the rise and fall typical of an ovulatory cycle, heart rate was lowest during the period. In the younger group, heart rate variability, or HRV, the small differences in time between heartbeats, was lower in the last days before the period than during it. Our article on [listening to your resting heart](https://www.sisly.ai/en/blog/listen-to-your-resting-heart/) explains what resting heart rate reflects. **Sleep.** The same study found no change across the cycle in sleep length, time to fall asleep, time awake in the night or how women rated their sleep. Mood was more positive around ovulation. The researchers noted that individual women may still have their own pattern. ## Do the Gulf heat and Ramadan affect how your cycle feels? The hormones are the same in Dubai or Riyadh as anywhere else. What the Gulf changes is the conditions around them. **Heat.** A long, hot summer can affect sleep and energy for anyone, and the days before and during a period can make that harder to carry. Cleveland Clinic's list of what moves resting temperature, including short sleep and stress, matters here: a hot, restless night is one of the things that can shift a reading. Our guides to [sleeping through a Gulf summer](https://www.sisly.ai/en/blog/sleeping-through-a-gulf-summer/) and [what 46 degrees does to you](https://www.sisly.ai/en/blog/what-46-degrees-does-to-you/) cover how the body copes with the heat. **Ramadan.** The holy month moves meal times and shortens many nights. Changes in sleep and routine can make your usual readings shift, so a week in Ramadan is worth comparing with the same week of an earlier cycle rather than with the week before it. Our article on [how Ramadan changes your sleep](https://www.sisly.ai/en/blog/how-ramadan-changes-your-sleep/) looks at those changes in more detail. ## How can you get to know your own cycle? Your own pattern is more useful than any average, and a few habits make it visible. 1. **Mark the first day of every period.** It is the anchor for everything else. 2. **Note how long each period lasts and how heavy it is.** A change in either is worth noticing. 3. **Write down symptoms and when they appear.** Bloating, tender breasts, headaches, cramps, low mood or trouble sleeping, with the date. 4. **Keep going for at least two or three cycles.** The NHS and ACOG both suggest a diary over this length of time. 5. **Note the unusual weeks.** Illness, travel, a very hot spell, fasting or stress all change how a cycle feels and what readings show. 6. **Compare each cycle with your own earlier ones.** Another woman's cycle length or symptoms say little about yours. 7. **Bring the record to a doctor if something changes.** Dates and notes are more useful than memory. ### Common mistakes when reading the phases - **Treating day 14 as fixed.** Ovulation moves with cycle length and can move from month to month. - **Reading one month as the rule.** A single long or short cycle is common; a change that stays is what matters. - **Using cycle tracking as contraception.** A wearable or an app on its own is not a method of contraception; the FAQ below gives the NHS figures for fertility awareness methods. - **Putting up with severe pain or very heavy bleeding.** Both are treatable, and both are reasons to see a doctor. ## When should you see a doctor about your cycle? The NHS advises seeing a doctor if: - you have missed three periods in a row, - your periods have not started by the age of 15, - your periods become irregular, heavier or more painful, - you bleed between periods, after sex or after the menopause, - period pain stops you doing your usual daily activities, - you have missed periods together with other changes, such as weight gain or loss, tiredness, new facial hair, or dry or oily skin. The NHS advises urgent help if pelvic or period pain is severe or worse than usual and painkillers have not helped. ACOG adds that premenstrual symptoms which disrupt your life can be treated, and that other conditions, such as depression, anxiety and thyroid disease, can look like PMS. A doctor can help tell them apart. If you would feel more at ease with a female doctor or gynaecologist, it is reasonable to ask for one when you book. ## Glossary of cycle terms - **Menstrual cycle:** the monthly cycle from the first day of one period to the day before the next. - **Endometrium:** the lining of the womb, which thickens each cycle and is shed as the period. - **Follicle:** a small sac in the ovary that holds an immature egg. - **Follicular phase:** the part of the cycle from the first day of the period to ovulation. - **FSH (follicle-stimulating hormone):** the hormone that starts follicles growing. - **Oestrogen:** a hormone that rises in the follicular phase and rebuilds the lining of the womb. - **LH (luteinising hormone):** the hormone whose surge triggers ovulation. - **Ovulation:** the release of a mature egg from the ovary. - **Corpus luteum:** the structure the empty follicle becomes after ovulation; it makes progesterone. - **Progesterone:** the hormone that keeps the lining of the womb ready in the luteal phase and raises resting temperature slightly. - **Luteal phase:** the part of the cycle from ovulation to the next period. - **PMS (premenstrual syndrome):** physical and emotional symptoms in the days before a period that return each cycle and affect daily life. - **Perimenopause:** the years before the menopause, when periods start to change. ## Where Sisly fits Sisly is a titanium ring or band that reads your sleep, energy, stress, heart rate variability, activity and skin temperature, each against your own normal. Over several cycles, that shows how your nights move across the month compared with your usual, rather than against an average. Your readings are hosted in the UAE, and the app is in Arabic and English. Sisly is not a medical device and not a method of contraception. The conclusions about your health belong to you and your doctor. ## FAQ **How many days is each phase of the menstrual cycle?** It varies from woman to woman. In a 28-day cycle, Cleveland Clinic describes the period in the first days, ovulation around day 14 and the luteal phase from about day 15 to day 28. In a 2019 study of more than 600,000 cycles, the follicular phase averaged 16.9 days and the luteal phase 12.4 days, with a wide spread around both. **Which phase of the cycle comes just before a period?** The luteal phase. It starts after ovulation and ends when the next period begins. The hormone progesterone is higher during this phase. If there is no pregnancy, hormone levels fall towards its end and the lining of the womb is shed as your period. Premenstrual symptoms such as bloating, tender breasts or mood changes usually appear in these days. **Is it normal for my cycle length to change from month to month?** Some change is common. The NHS says cycles of 21 to 35 days are common, and a large 2019 study found that the follicular phase, the part before ovulation, varies the most. Cycles also tend to shorten slightly with age. A cycle that becomes irregular for several months, or a period that stops, is worth discussing with a doctor. **Does ovulation always happen on day 14?** No. Day 14 is a textbook figure for a 28-day cycle. The NHS says ovulation happens about 12 to 16 days before the next period starts, so its day depends on your cycle length. A 2000 study in the BMJ found that the timing of the fertile days varied widely, even in women whose cycles were usually regular. **Why do I feel warmer or sleep differently before my period?** After ovulation, basal body temperature rises by about 0.2 to 0.6°C, according to Cleveland Clinic, and usually falls again before your period. A 2024 study of women wearing a ring found heart rate was lowest during the period. Sleep length and quality did not change across the cycle in that study, though individual women may notice differences. **Can tracking my cycle phases prevent pregnancy?** Not on its own, and not from a consumer wearable. The NHS says fertility awareness methods are 91 to 99% effective when taught by a trained professional and followed exactly, and about 76% effective when they are not. Those methods combine temperature, discharge and cycle length. Speak to a doctor about contraception that suits you. **When should I see a doctor about my periods?** The NHS advises seeing a doctor if you miss three periods in a row, if your periods have not started by 15, if they become irregular, heavier or more painful, or if you bleed between periods, after sex or after the menopause. Pain that stops your usual day, or that painkillers do not ease, is also a reason to go.