A normal period lasts between two and eight days, with most people bleeding for four to six days. If your period is stretching beyond eight days, or if it’s noticeably longer than what’s typical for you, something is shifting the balance of hormones, uterine tissue, or clotting factors that normally keep bleeding on schedule. The cause can range from a temporary hormonal blip to something that needs medical attention, and narrowing it down depends on your age, other symptoms, and what else is going on in your body.
How Your Body Normally Stops a Period
Understanding why a period drags on starts with understanding what ends it. During the first half of your cycle, estrogen thickens the lining of your uterus. After ovulation, progesterone takes over and stops that growth, essentially putting the brakes on. When progesterone drops at the end of the cycle, that thick lining sheds in an organized way, and bleeding wraps up within a few days.
Anything that disrupts this sequence, whether it’s a month where you didn’t ovulate, a structural problem inside the uterus, or a medical condition affecting your hormones or blood clotting, can make bleeding last longer than it should.
Anovulatory Cycles and Hormonal Imbalance
The most common reason for a prolonged period is a cycle where you didn’t ovulate. Without ovulation, your body never produces the progesterone needed to counterbalance estrogen. The uterine lining keeps thickening under estrogen’s influence, and when it finally breaks down, there’s more tissue to shed and no coordinated signal telling it when to stop. The result is bleeding that’s heavier, longer, or irregular.
Anovulatory cycles happen to most people occasionally, often triggered by stress, illness, significant weight changes, or disrupted sleep. But they’re also a hallmark of polycystic ovary syndrome (PCOS). In PCOS, excess androgens are converted into estrogen in fat tissue, creating prolonged periods of unopposed estrogen acting on the uterine lining. The lining grows thick before bleeding begins and lacks the progesterone-driven process that normally makes shedding quick and complete. This can cause periods that last well over a week, sometimes with ongoing spotting between them.
Perimenopause Changes
If you’re in your late 30s or 40s, perimenopause is one of the likeliest explanations. As you approach menopause, your cycles become less predictable. Population studies show that both very short cycles (under 21 days) and very long cycles become more common during this transition. The frequency of bleeding episodes lasting 10 or more days increases, along with more spotting and wider swings in flow from one month to the next.
What’s happening hormonally is complex. Estrogen levels can actually spike higher than normal during perimenopause, and research from the Study of Women’s Health Across the Nation found that blood loss exceeding 200 mL was linked to high estrogen levels in ovulatory cycles. At the same time, anovulatory cycles become more frequent, especially in early perimenopause, and those are associated with spotting and bleeding lasting more than eight days. So whether you’re still ovulating or not, the hormonal instability of this phase can extend your periods significantly.
Fibroids, Polyps, and Adenomyosis
Structural changes inside the uterus are another major category. Uterine fibroids are noncancerous growths in or on the uterine wall that are extremely common, particularly after age 30. Fibroids that grow into the uterine cavity can distort the lining, increase the surface area that bleeds, and interfere with the uterus’s ability to contract and clamp down on blood vessels, which is part of how bleeding normally stops. Endometrial polyps, small overgrowths of the lining itself, cause similar problems on a smaller scale.
Adenomyosis is a condition where tissue that normally lines the inside of the uterus grows into the muscular wall. That displaced tissue still thickens, breaks down, and bleeds with each cycle, but it’s trapped within the muscle. This makes the uterus enlarge over time and often causes periods that are both heavier and longer. Adenomyosis is most common in people who’ve had children or uterine surgery, though it can occur in anyone.
Your IUD or Medications
A copper IUD is well known for making periods longer and heavier. Research shows copper IUDs increase menstrual blood loss by about 50% over pre-insertion levels, and this increase stays fairly constant through at least the first year. In one study, 60% of copper IUD users reported heavier flow, and 50% reported more days of bleeding. Average bleeding duration hovered around six days across the first year, but individual variation was wide.
Blood thinners (anticoagulants) can also extend period length by slowing down your body’s ability to form clots at the uterine lining. Some hormonal medications, including certain types of hormonal birth control, can cause breakthrough bleeding or prolonged spotting, especially in the first few months of use or if pills are missed.
Thyroid Problems and Bleeding Disorders
An underactive thyroid (hypothyroidism) can quietly lengthen your periods through two separate pathways. First, low thyroid hormone disrupts the signaling between your thyroid and reproductive hormones, altering estrogen and progesterone levels. Second, hypothyroidism shifts your blood’s clotting system toward bleeding more easily. It reduces the production of key clotting proteins and can trigger acquired von Willebrand syndrome, a condition where your blood simply doesn’t clot as efficiently. Both effects together can make periods noticeably longer and heavier, and they resolve once thyroid levels are corrected with medication.
Inherited bleeding disorders are an underrecognized cause of long, heavy periods. Von Willebrand disease, the most common inherited bleeding disorder, affects the same clotting protein that hypothyroidism disrupts. Among people with chronically heavy menstrual bleeding, somewhere between 5% and 24% have von Willebrand disease. If your periods have always been heavy and long, and you also bruise easily or bleed a lot from dental work or minor cuts, a bleeding disorder is worth investigating.
When Prolonged Bleeding Signals a Problem
A single long period after a stressful month or a skipped ovulation isn’t necessarily alarming. But certain patterns deserve prompt attention. Soaking through a pad or tampon every one to two hours, or going through three fully soaked pads (or six regular tampons) per day for three or more days, meets the clinical definition of heavy menstrual bleeding. Periods consistently lasting beyond eight days, bleeding between periods, or bleeding after menopause all warrant evaluation.
Prolonged unopposed estrogen exposure doesn’t just cause inconvenient bleeding. Over time, it can lead to excessive thickening of the uterine lining, a condition called endometrial hyperplasia, which carries an increased risk of uterine cancer. This is one reason persistent abnormal bleeding gets taken seriously rather than written off as a nuisance.
How the Cause Gets Identified
Figuring out why your period is lasting longer than normal typically starts with blood work to check hormone levels (including thyroid function) and a complete blood count to assess whether you’re becoming anemic from the extra blood loss. A transvaginal ultrasound can measure the thickness of your uterine lining and identify fibroids or polyps. A thin, normal lining on ultrasound (4 mm or less in postmenopausal patients) has a greater than 99% negative predictive value for uterine cancer, making it a reassuring first step.
If the ultrasound doesn’t explain the bleeding, or if the lining appears thickened, the next step is usually an endometrial biopsy, a brief in-office procedure where a small sample of the lining is collected and examined under a microscope. For bleeding that persists despite a normal biopsy, a more detailed look with a hysteroscopy (a tiny camera inserted through the cervix) can catch small polyps or other abnormalities that imaging might miss. If you have symptoms suggesting a bleeding disorder, specific blood tests for von Willebrand factor and clotting proteins can confirm or rule that out.