A normal period lasts between 2 and 7 days. If yours regularly stretches past that 7-day mark, something is disrupting the usual process of building up and shedding your uterine lining. The cause could be as straightforward as a hormonal shift or as specific as a structural change in your uterus. Either way, periods lasting longer than 7 days are classified as heavy menstrual bleeding and worth investigating.
Hormonal Imbalance Is the Most Common Cause
Your period depends on a precise back-and-forth between two hormones: estrogen and progesterone. Estrogen thickens the lining of your uterus in the first half of your cycle, and progesterone stabilizes it after ovulation. When you have too much estrogen relative to progesterone, the lining grows thicker than it should. A thicker lining takes longer to shed, which means more days of bleeding.
This imbalance often happens when you don’t ovulate during a cycle. Without ovulation, your body never produces the progesterone surge that would normally keep the lining in check. The lining continues to build under estrogen’s influence, then sheds unpredictably and for longer than usual. Skipped ovulation is especially common in two stages of life: the first few years after your period starts and the years leading up to menopause, when women may go months without ovulating.
Thyroid Problems and PCOS
An underactive thyroid slows down processes throughout your body, and your menstrual cycle is no exception. Low thyroid hormone suppresses the signals your brain sends to your ovaries, which can prevent ovulation entirely. It also raises levels of a hormone called prolactin, which interferes with estrogen production and throws off your cycle’s regularity. On top of that, low thyroid function changes how your blood clots, which can lead to heavier, longer-lasting bleeding and excessive thickening of the uterine lining.
Polycystic ovary syndrome (PCOS) works through a similar mechanism. Women with PCOS frequently don’t ovulate on a regular schedule, so the uterine lining builds up over weeks or even months without progesterone to stabilize it. When bleeding finally arrives, it can be prolonged and heavy because there’s simply more lining to shed.
Fibroids, Polyps, and Adenomyosis
Sometimes the issue isn’t hormonal but structural. Uterine fibroids are noncancerous growths in the muscle wall of the uterus. They can distort the uterine cavity and increase the surface area of the lining, which leads to longer, heavier periods. Fibroids are extremely common, particularly in women over 30.
Uterine polyps are a different type of growth. These form when cells in the uterine lining overgrow and create soft projections that attach to the inner wall by a base or thin stalk. Polyps can cause irregular bleeding, very heavy flow, and bleeding between periods.
Adenomyosis is a condition where tissue that normally lines the uterus grows into the muscular wall instead. During your period, that embedded tissue thickens, breaks down, and bleeds just like the regular lining does, but it’s trapped within the muscle. This causes heavy or prolonged periods along with severe cramping and pelvic pain that can persist even between cycles. Over time, the heavy bleeding from adenomyosis can lead to anemia.
Your Birth Control Could Be a Factor
If your periods got longer after getting a copper IUD, that’s a well-documented side effect. The copper IUD doesn’t use hormones, so it doesn’t suppress your natural cycle, but it does cause inflammation in the uterus that can make periods heavier, longer, and more painful. These side effects typically ease up after three to six months. If they don’t, or if bleeding is severe, it may be worth discussing alternatives.
Switching between hormonal birth control methods or stopping them altogether can also temporarily change your period length as your body readjusts its hormone levels.
Bleeding Disorders Are Underdiagnosed
This is the cause most people don’t think about. Von Willebrand disease is the most common inherited bleeding disorder in women, affecting roughly 1 in 100. But among women who experience chronically heavy periods, the prevalence jumps to between 5% and 24%. Among those with the condition, 74% to 92% report heavy menstrual bleeding as a symptom.
The clue that a bleeding disorder might be involved is a pattern of bleeding problems beyond just your period. If you also deal with frequent nosebleeds, gums that bleed easily, heavy bleeding after dental work, or prolonged bleeding from minor cuts, those are signs worth mentioning to your provider. A screening guideline from the American College of Obstetricians and Gynecologists flags heavy periods since your very first cycle, combined with any surgical or dental bleeding, as criteria for further evaluation.
Signs Your Bleeding Needs Attention Now
The CDC considers any period longer than 7 days to be heavy bleeding. Beyond duration, pay attention to volume. You should talk with a provider if you:
- Need to change your pad or tampon more often than every 2 hours
- Soak through one or more pads or tampons per hour for several consecutive hours
- Have to double up on pads to manage the flow
- Wake up at night to change pads or tampons
- Pass blood clots the size of a quarter or larger
What Iron Loss Actually Feels Like
One of the biggest consequences of prolonged periods is iron deficiency anemia, and it develops so gradually that many women don’t realize it’s happening. Every extra day of bleeding drains iron from your body. Over months, your iron stores (measured by a protein called ferritin) drop, and your blood’s ability to carry oxygen declines.
The symptoms are easy to dismiss or attribute to stress: constant fatigue, weakness, dizziness, and feeling short of breath during activities that didn’t used to wind you. If your periods have been running long and you recognize those symptoms, a blood test checking your hemoglobin and ferritin levels can confirm whether iron loss is the problem. It’s worth knowing that a normal ferritin result doesn’t always rule out iron deficiency, since ferritin levels can appear falsely elevated when your body is fighting inflammation.
What to Expect at a Medical Visit
When you bring up prolonged periods, your provider will likely start with blood work to check for anemia, iron stores, thyroid function, and possibly markers of a bleeding disorder. For adult women, an ultrasound can identify fibroids, polyps, or signs of adenomyosis. For teens, routine ultrasound usually isn’t the first step unless initial treatment doesn’t help.
Tracking your cycle before your appointment makes the conversation more productive. Note how many days you bleed, how often you change your pad or tampon, whether you pass clots, and any pain you experience. That information helps your provider distinguish between a hormonal issue, a structural cause, and a bleeding disorder, which each point toward different treatment paths.