Your menstrual cycle is the monthly sequence of hormonal changes your body goes through to prepare for a possible pregnancy. It starts on the first day of your period and ends the day before your next one begins. A typical cycle lasts 28 days, but anything from 24 to 38 days is considered regular. Understanding what happens during each phase helps you make sense of the physical and emotional shifts you experience throughout the month.
The Four Phases of Your Cycle
The menstrual cycle has four distinct phases, each driven by different hormones and serving a specific purpose.
Menstruation (days 1 to roughly 5): This is your period. The uterine lining sheds because no pregnancy occurred in the previous cycle. Most periods involve less than 45 mL of blood loss, which is less than three tablespoons. Anything under 60 mL is clinically normal, while consistently losing more than 100 mL per period is considered excessive.
Follicular phase (days 1 through ovulation): This phase overlaps with menstruation and continues after your period ends. Your brain’s pituitary gland releases a hormone that stimulates several follicles in your ovaries to grow, each containing one egg. As these follicles develop, they produce rising levels of estrogen, which thickens the uterine lining in preparation for a potential pregnancy. By about day seven, estrogen levels climb high enough to signal most of the smaller follicles to stop growing, leaving one dominant follicle to continue maturing.
Ovulation (around day 14): When estrogen reaches a critical threshold, it triggers a sharp spike of luteinizing hormone, usually around day 13. This surge causes the mature follicle to release its egg into the fallopian tube. You have about six fertile days per cycle: the five days before ovulation (because sperm can survive that long inside the reproductive tract) and the day of ovulation itself.
Luteal phase (ovulation through the end of the cycle): After the egg is released, the empty follicle transforms into a structure called the corpus luteum, which pumps out progesterone. This hormone creates a richly blood-supplied uterine lining ideal for a fertilized egg to implant. If no implantation occurs, the corpus luteum breaks down, progesterone drops, and the lining sheds as your next period. The luteal phase is relatively consistent at about 14 days, regardless of your overall cycle length.
How Hormones Drive the Whole Process
Four hormones do most of the work. Follicle-stimulating hormone (FSH) kicks things off by telling your ovaries to develop egg-containing follicles. As those follicles grow, they produce estrogen, which thickens the uterine lining and eventually signals your brain to release a burst of luteinizing hormone (LH). That LH surge is what triggers ovulation. After the egg is released, progesterone takes over, maintaining the uterine lining and keeping the environment stable for potential implantation.
These hormones don’t just operate independently. They form a feedback loop: rising estrogen suppresses FSH so only one dominant follicle survives, and falling progesterone at the end of the luteal phase is what restarts the whole cycle. This is why hormonal disruptions at any point can ripple through the entire month.
Physical and Emotional Changes by Phase
The follicular phase, from your period through ovulation, is hormonally stable, particularly in terms of progesterone. Many people feel their best during this stretch, with gradually increasing energy as estrogen rises.
The luteal phase is a different story. The fluctuations in estrogen and progesterone after ovulation are responsible for premenstrual symptoms. Gastrointestinal issues like bloating, constipation, and nausea are reported significantly more often during this phase, affecting as many as 73% of menstruating people in the days before their period. Mood changes and gut symptoms tend to track together: when one worsens, the other often does too.
About 20% of menstruating people experience premenstrual syndrome (PMS), a recognizable cluster of symptoms in the week before their period. These can include anxiety, irritability, depression, breast tenderness, headaches, joint or muscle pain, and bloating. A smaller percentage experience premenstrual dysphoric disorder (PMDD), a more severe form that requires at least five symptoms, predominantly mood-related, along with noticeable difficulty functioning in daily life.
How Your Cycle Changes With Age
Cycles don’t behave the same way at every stage of life. In the first year or two after a person’s first period, cycles are often irregular. The pituitary gland and ovaries are still learning to coordinate, hormone levels shift rapidly, and ovulation may not happen at all during some early cycles. This is normal and typically resolves within a few years.
During the late 40s, the transition toward menopause (perimenopause) brings another round of changes. The remaining eggs produce less estrogen, which causes the pituitary gland to ramp up FSH to compensate. Higher FSH levels trigger ovulation earlier in the cycle, so cycles often shorten to around 21 days. Skipped periods become common as ovulation becomes less reliable, and cycle length can vary widely from month to month before periods stop entirely.
How to Track Your Cycle
The simplest approach is the calendar method. Mark the first day of each period on a calendar or app, then count the days between start dates. After six months of tracking, you’ll have a reliable picture of your shortest and longest cycles. To estimate your fertile window, subtract 18 from your shortest cycle length to find the first fertile day, and subtract 11 from your longest cycle to find the last.
Basal body temperature offers another layer of information. Take your temperature each morning before getting out of bed, using a thermometer that reads to two decimal places. After ovulation, your temperature rises by 0.4 to 1 degree Fahrenheit (0.22 to 0.56 degrees Celsius). Charting this daily reveals a clear pattern over time, though the temperature shift confirms ovulation after it has already happened rather than predicting it in advance.
Cervical mucus tracking is a third option. By checking your mucus daily and recording the texture and amount, you can identify a pattern tied to your fertile window. In the days leading up to ovulation, mucus typically becomes clearer, more slippery, and stretchy. Combining all three methods gives the most complete picture of your cycle.
Signs Your Cycle May Need Attention
Not every irregular period signals a problem, but certain patterns are worth paying attention to. Cycles that consistently fall shorter than 21 days or longer than 35 days, missing three or more periods in a row, and cycles that vary by more than nine days in length from month to month all fall outside the normal range.
Specific symptoms to take seriously include soaking through a pad or tampon every hour for two to three hours, passing blood clots larger than a quarter, periods lasting longer than seven days, severe pain during or between periods, bleeding or spotting between periods or after menopause, and foul-smelling vaginal discharge. Any of these can point to conditions that benefit from evaluation and treatment.