A normal period lasts about 4 to 5 days, and anything beyond 7 days is considered medically prolonged. If your period keeps going past that point, or if it’s gradually gotten longer over time, several things could be behind it, from hormonal shifts to structural changes in the uterus to an underlying bleeding disorder. The cause often depends on your age, whether you use contraception, and what other symptoms show up alongside the longer bleeding.
What Counts as Too Long
Most people lose about 2 to 3 tablespoons of blood during a period. When bleeding stretches past 7 days, blood loss roughly doubles, which is enough to drain your iron stores over several cycles. A period that consistently runs 8, 9, or 10 days isn’t just inconvenient. It’s a signal that something is affecting how your uterine lining builds up, breaks down, or clots.
Hormonal Imbalance Is the Most Common Cause
Your menstrual cycle relies on a precise back-and-forth between two hormones. In the first half of the cycle, estrogen thickens the uterine lining to prepare for a possible pregnancy. After ovulation, progesterone rises and stabilizes that lining. If pregnancy doesn’t happen, both hormones drop, and the lining sheds in an organized way. That organized shedding is a normal period.
The problem starts when you don’t ovulate. Without ovulation, progesterone never kicks in, so estrogen keeps building the lining unopposed. The lining grows thicker than it should, and when it finally breaks down, it sheds unevenly and slowly. This is one of the most frequent reasons for prolonged bleeding, and it can happen to anyone, though it’s especially common at two points in life: the first few years after periods start, and the years leading up to menopause.
In more persistent cases, that ongoing estrogen exposure without progesterone can lead to a condition called endometrial hyperplasia, where the lining cells become overcrowded and potentially abnormal. This doesn’t always cause symptoms beyond long or heavy periods, which is why it often goes undetected without an evaluation.
Perimenopause Changes the Rules
If you’re in your late 30s or 40s and your periods are suddenly lasting longer, becoming unpredictable, or arriving with what feels like flooding, perimenopause is a likely explanation. During this transition, ovulation becomes inconsistent. Some cycles you’ll ovulate normally, others you won’t ovulate at all. In cycles without ovulation, progesterone stays low, the lining keeps thickening under estrogen’s influence, and the eventual bleed is heavier and longer than usual.
This pattern can go on for years before periods stop entirely. The bleeding can vary wildly from one cycle to the next, with a 5-day period one month followed by a 10-day one the next. That unpredictability is a hallmark of the perimenopausal transition, but it still warrants a check-in with your doctor because other conditions can look similar.
Structural Problems in the Uterus
Sometimes prolonged bleeding has a physical cause. Fibroids, which are noncancerous growths in or on the uterine wall, can distort the lining and increase the surface area that bleeds. Polyps, small tissue growths on the inner wall of the uterus, can also extend bleeding by creating extra tissue that sheds irregularly.
Adenomyosis is another structural cause that’s often overlooked. In this condition, the tissue that normally lines the uterus grows into the muscular wall itself. During your period, that embedded tissue thickens, breaks down, and bleeds just like the normal lining does, but it’s trapped within the muscle. This causes the uterus to enlarge and leads to prolonged, heavy, and often painful periods. Adenomyosis is most common in people who’ve had children or uterine surgery, though it can occur without those risk factors.
Bleeding Disorders
Long, heavy periods are sometimes the only visible sign of an underlying blood clotting disorder. Von Willebrand disease, the most common inherited bleeding disorder, affects how well your blood forms clots. Among people with chronic heavy menstrual bleeding, somewhere between 5% and 24% have this condition, yet many go undiagnosed for years because heavy periods are often dismissed as normal variation.
If your periods have been long and heavy since they first started, if you bruise easily, bleed a lot after dental work, or have a family history of bleeding problems, a clotting disorder is worth investigating. A blood test can identify most of these conditions.
Your IUD Could Be a Factor
Copper IUDs are a well-known cause of longer, heavier periods. Because they contain no hormones, they don’t thin the uterine lining the way hormonal options do. Many people with copper IUDs notice their periods become heavier and crampier, particularly in the first few months after insertion. This typically improves over time, but for some people the change persists.
Hormonal IUDs tend to have the opposite long-term effect, often making periods lighter or stopping them altogether. However, in the first 3 to 6 months after insertion, irregular and sometimes prolonged light bleeding is common as your body adjusts.
The Iron Problem
Losing more blood each cycle means losing more iron, and your body may not be able to replace it fast enough through diet alone. Iron deficiency is diagnosed when a blood marker called ferritin drops below 30, and treatment is recommended at that threshold. But iron depletion is a gradual process, so you can feel the effects well before your levels fall into the “anemic” range. Fatigue, brain fog, shortness of breath during exercise, restless legs, and hair thinning are all signs your iron stores are running low.
If your periods have been running long for several months or more, it’s worth asking for a ferritin test specifically. Standard blood work often only checks hemoglobin, which doesn’t drop until iron deficiency is already advanced. A ferritin below 50 already corresponds with abnormal markers of iron depletion, and treatment targets are typically 50 or higher for oral supplementation and 100 or higher for IV iron in people who are at greater risk of rapid depletion.
Signs That Need Prompt Attention
Some patterns of prolonged bleeding point to something that needs evaluation sooner rather than later. Bleeding that soaks through a pad or tampon every hour for several consecutive hours, passing clots larger than a quarter, bleeding that makes you feel lightheaded or short of breath, or any bleeding after menopause are all reasons to contact your doctor without waiting for the next cycle to see if things improve. A period that gradually creeps from 5 days to 9 or 10 over several months is also worth discussing, even if the flow itself doesn’t feel alarming, because the underlying cause is easier to address when caught early.