Periods that stretch beyond their usual length often signal a shift in hormones, though structural changes in the uterus and other medical conditions can also be responsible. A typical period lasts about 4 to 5 days, and anything consistently longer than 7 days is considered prolonged. If your periods have recently started lasting longer than what’s normal for you, several common causes are worth understanding.
What Counts as a Long Period
Most people lose only about 2 to 3 tablespoons of blood during a period. When bleeding extends past 7 days, or when you’re soaking through a pad or tampon nearly every hour, that crosses into heavy or prolonged territory. But even a shift from your personal baseline matters. If your periods reliably lasted 4 days and now regularly stretch to 6, something has changed, even if you’re still technically within the “normal” window.
Hormonal Shifts Are the Most Common Cause
Your period depends on a carefully timed rise and fall of estrogen and progesterone. After you ovulate, progesterone stabilizes the uterine lining and prepares it for a controlled shed. When ovulation doesn’t happen (a cycle called anovulatory), your body never produces that progesterone signal. Without it, the uterine lining keeps thickening under the influence of estrogen alone. When it finally breaks down, the shedding is uneven and can drag on for days longer than usual.
Anovulatory cycles are especially common at two points in life: the first few years after periods start and the years leading up to menopause. During perimenopause, estrogen and progesterone fluctuate unpredictably. Ovulation becomes less reliable, which means some cycles produce plenty of progesterone and others produce very little. The result is periods that vary wildly from month to month. Your flow may be light one cycle and heavy the next, or you may skip a period entirely and then have one that lasts over a week.
Stress, significant weight changes, and excessive exercise can also disrupt ovulation in the same way, leading to longer or irregular bleeding at any age.
Structural Changes in the Uterus
Sometimes the issue isn’t hormonal but physical. Growths or changes in the uterus itself can increase the surface area that bleeds or interfere with the uterus’s ability to contract and stop bleeding efficiently.
- Polyps are small, soft growths on the uterine lining. They’re usually noncancerous but can cause bleeding between periods and make periods themselves last longer.
- Fibroids are muscular growths in or on the uterine wall. They’re extremely common, and depending on their size and location, they can lead to prolonged, heavy periods.
- Adenomyosis occurs when tissue that normally lines the uterus grows into the muscular wall. This makes the uterus larger and spongier, which often causes both heavier and longer periods along with significant cramping.
These structural causes tend to develop gradually, so you might notice your periods creeping longer over several months rather than changing overnight. They’re typically identified through imaging. A standard transvaginal ultrasound is usually the first step, but if the results aren’t clear enough, a sonohysterogram (which uses a small amount of saline to expand the uterine cavity during the ultrasound) gives a sharper picture of polyps, fibroids, and scarring inside the uterus.
Thyroid Problems
Your thyroid gland influences nearly every system in your body, including your menstrual cycle. An underactive thyroid (hypothyroidism) is a well-established cause of heavier, longer periods. Studies have found that roughly half or more of people with hypothyroidism experience some form of menstrual irregularity, with prolonged or heavy bleeding being one of the most common patterns. The exact mechanism isn’t fully understood, but thyroid hormones interact directly with reproductive hormones, and when thyroid levels drop, the downstream effects on your cycle can be significant.
Other signs of an underactive thyroid include fatigue, weight gain, feeling cold all the time, dry skin, and brain fog. If longer periods showed up alongside any of these symptoms, a simple blood test can check your thyroid function.
Bleeding Disorders
This is a cause many people never consider, but it’s more common than you’d think. Von Willebrand disease is the most common inherited bleeding disorder in women, affecting roughly 1 in 100. Among women specifically seeking help for chronic heavy periods, the prevalence jumps to between 5% and 24%.
Von Willebrand disease affects the blood’s ability to clot properly. If you’ve had heavy or long periods since your very first one, and you also have a history of frequent nosebleeds, gums that bleed easily, excessive bleeding after dental work or surgery, or a family member with similar symptoms, it’s worth bringing up with your doctor. Diagnosis requires specialized blood tests and sometimes repeat testing, since results can fluctuate.
Medications and Birth Control
Certain medications can make periods longer as a direct side effect. The copper IUD is one of the most well-known culprits. Unlike hormonal IUDs, the copper IUD contains no hormones and works by creating an inflammatory response in the uterus. This commonly leads to heavier, longer, and more painful periods, especially in the first several months. These side effects often ease up after three to six months, but for some people they persist.
Blood thinners (anticoagulants) can also extend bleeding duration. If you recently started any new medication and noticed your periods changing, the timing is worth noting.
When Longer Periods Lead to Anemia
Prolonged periods aren’t just inconvenient. They can deplete your iron stores over time. About one in five women have heavy periods, and this group is at especially high risk for iron deficiency. Your body uses iron to make red blood cells, and when you lose more blood each month than your body can easily replace, the deficit builds gradually.
Iron deficiency often creeps up slowly enough that you adjust to feeling tired without realizing something is off. Watch for persistent fatigue that rest doesn’t fix, shortness of breath during activities that used to feel easy, dizziness, pale skin, and brittle nails. If your periods have been running long for several months, checking your iron levels is a practical step.
What to Pay Attention To
Tracking your cycle for a few months gives you and your doctor much more to work with than a vague sense that things have changed. Note how many days you bleed, how heavy the flow is each day, and whether you’re passing clots. Clots larger than a quarter are worth mentioning specifically.
A single longer-than-usual period can be a one-off hormonal blip, especially if you’ve been stressed, sick, or traveling. But if the pattern repeats for two or three cycles, or if you’re soaking through protection every hour, bleeding between periods, or feeling symptoms of anemia, those are signals your body is asking for attention. The evaluation process typically starts with blood work and an ultrasound, both of which are straightforward and noninvasive.