A normal period comes every 21 to 35 days, with most people landing somewhere around 28 days. The bleeding itself typically lasts 2 to 7 days. Those ranges are wide because “normal” varies significantly from person to person, and even from cycle to cycle in the same person.
How Cycle Length Is Counted
Your cycle length is the number of days from the first day of one period to the first day of the next. Day 1 is the first day of actual bleeding, not spotting. So if your period starts on March 3 and your next period starts on March 31, that cycle was 28 days long.
Tracking a few cycles gives you a much clearer picture than relying on a single month. Your cycles don’t need to be exactly the same length every time. Variation of up to 7 to 9 days between cycles is still considered regular. If one month is 26 days and the next is 32, that’s within the normal window.
How Frequency Changes With Age
Periods don’t follow the same schedule throughout your life. For the first few years after menstruation begins (usually between ages 10 and 15), longer and more unpredictable cycles are common. The body is still establishing a hormonal rhythm, so cycles of 40 or even 45 days aren’t unusual for teenagers. Most people settle into a more predictable pattern within two to three years of their first period.
During the main reproductive years, roughly the mid-20s through the late 30s, cycles tend to be at their most consistent. Then as you approach menopause, typically in your 40s, cycles often become irregular again. Periods may come closer together, further apart, or skip months entirely. This transitional phase, called perimenopause, can last several years before periods stop altogether.
How Long Bleeding Lasts
Most periods last between 3 and 5 days, though anything from 2 to 7 days falls within the normal range. Flow is usually heaviest during the first day or two, then gradually tapers off. A period that consistently lasts longer than 7 days is worth looking into, as it may signal a hormonal imbalance or another underlying issue.
What Makes Periods Irregular
A period is considered irregular when your cycle is consistently shorter than 21 days, longer than 35 days, or varies by more than 7 to 9 days from one cycle to the next. Missing your period entirely for 3 to 6 months (without pregnancy) also counts.
Everyday lifestyle factors are some of the most common causes of irregular periods. Stress can delay or skip ovulation, pushing your period back. Significant weight gain or loss disrupts the hormones that regulate your cycle. Intense exercise routines that result in very low body fat, common among long-distance runners, dancers, and gymnasts, can cause periods to become infrequent or stop altogether.
Several medical conditions also affect period frequency:
- Polycystic ovary syndrome (PCOS) causes the ovaries to produce excess androgens, a type of hormone that prevents or delays ovulation. This leads to irregular, infrequent, or completely absent periods. PCOS is one of the most common reasons for missed periods in people of reproductive age.
- Thyroid disorders directly affect the hormones that control your cycle. Both an underactive and overactive thyroid can make periods irregular, heavier, lighter, or less frequent.
- Primary ovarian insufficiency occurs when the ovaries stop functioning normally before age 40, leading to missed or irregular periods.
- Endometriosis involves uterine lining tissue growing outside the uterus, often on the ovaries or fallopian tubes, and can disrupt cycle regularity.
Signs Your Cycle May Need Attention
Some variation is completely normal. But certain patterns suggest something beyond ordinary fluctuation. Cycles consistently shorter than 21 days or longer than 35 days fall outside the standard range. Bleeding that lasts more than 7 days, soaking through a pad or tampon every hour for several hours, or sudden changes to a cycle that had been predictable are all worth noting.
Going three months or more without a period when you’re not pregnant, breastfeeding, or approaching menopause is another signal that something hormonal or medical may be going on. The same applies if your cycle length swings wildly, say 24 days one month and 42 the next, on a regular basis.