A normal menstrual cycle ranges from 21 to 35 days in adults, counted from the first day of one period to the first day of the next. Bleeding itself typically lasts 2 to 7 days. But those numbers are averages across a wide population, and your own “normal” can shift depending on your age, whether you’re ovulating regularly, and where you are in your reproductive years.
How to Count Your Cycle Length
Day 1 of your cycle is the first day you notice bleeding, not spotting. Your cycle length is the number of days from that Day 1 to the day before your next period starts. So if you start bleeding on March 3 and your next period arrives on March 31, that cycle was 28 days.
The often-cited “28-day cycle” is a useful reference point, but it’s not the standard everyone should expect. Cycles anywhere from 21 to 35 days are considered normal for adults. Tracking three to six consecutive cycles gives you a much clearer picture of your personal pattern than any single month can.
What Happens During Each Phase
Your cycle has two main halves, separated by ovulation.
The first half, called the follicular phase, starts on Day 1 of bleeding and lasts until ovulation. During this phase, your body prepares an egg for release while simultaneously thickening the uterine lining. This phase is the variable one, ranging from about 14 to 21 days, which is why total cycle length differs so much from person to person.
Ovulation happens when a surge of luteinizing hormone (LH) triggers the release of an egg. That surge occurs roughly 24 to 48 hours before the egg is actually released. In a 28-day cycle, ovulation typically falls around Day 14, but in a shorter 24-day cycle it can happen as early as Day 10 or 11. If you’re tracking ovulation for fertility or awareness, knowing your own cycle length matters more than memorizing “Day 14.”
The second half, the luteal phase, runs from ovulation to the start of your next period and is remarkably consistent at about 14 days. During this stretch, progesterone rises to maintain the uterine lining. If the egg isn’t fertilized, progesterone drops and the lining sheds. That shedding is your period.
How Much Bleeding Is Normal
Most people lose less than 60 milliliters of blood during a period, which is roughly 4 tablespoons spread over several days. That amount often feels like more than it is because menstrual fluid also contains tissue and mucus alongside actual blood.
Heavy menstrual bleeding is generally defined as losing more than 80 milliliters per cycle. Practical signs that bleeding may be heavier than normal include soaking through a pad or tampon every hour for several consecutive hours, needing to change protection overnight, passing blood clots larger than a quarter, or having periods that consistently last longer than 7 days. Bleeding in the 60 to 100 milliliter range is considered moderately heavy and worth paying attention to, especially if it’s a change from your usual pattern.
How Your Cycle Changes With Age
Adolescence
Periods in the first year or two after they start are often irregular. The hormonal communication system between the brain and ovaries is still maturing, and many early cycles don’t include ovulation at all. During this time, cycles can range from 21 to 45 days and still be considered within the expected range. About 90% of adolescent cycles fall within that window. It typically takes a year or more before cycles settle into a more predictable rhythm.
Your 20s and 30s
This is when cycles tend to be most regular. The follicular phase stabilizes, ovulation becomes more predictable, and most cycles cluster in the 21 to 35 day range. Variation of a few days from month to month is completely normal, though. A cycle that’s 26 days one month and 30 the next doesn’t signal a problem.
Your 40s and Perimenopause
Starting in the mid to late 40s, cycles often become irregular again. The remaining eggs produce less estrogen, which causes the brain to release more follicle-stimulating hormone (FSH) to compensate. This can trigger ovulation earlier in the cycle, shortening it to around 21 days. As the transition to menopause continues, skipped cycles become common as ovulation stops happening every month. Some months you may bleed heavily, others barely at all. This phase can last several years before periods stop entirely.
Signs Your Cycle May Need Attention
Occasional variation is expected, but certain patterns are worth investigating. Cycles that consistently fall shorter than 21 days or longer than 35 days in adults (or longer than 45 days in teens) may signal a hormonal imbalance, thyroid issue, or a condition like polycystic ovary syndrome. Periods that suddenly become much heavier, much lighter, or significantly more painful than your established pattern also deserve a closer look.
If you go 90 days or more without a period and you’re not pregnant, breastfeeding, or using hormonal contraception, that’s a signal worth acting on. The same applies if bleeding regularly lasts longer than 7 days or if you notice bleeding between periods. Tracking your cycles, even with a simple calendar or phone app, gives you and your healthcare provider real data to work with instead of relying on memory.