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Bleeding for only 1 day each month sounds convenient, especially since the average period lasts 4 to 8 days. But a sudden change in your menstrual cycle can make you wonder whether a 1-day period is a reason to be concerned or truly NBD.

Plenty of things can be responsible for spotting or a 1-day period, including pregnancy (surprise!), birth control, medications, or certain medical conditions. Excessive exercise, your age, and weight loss can also be behind your abbreviated bleed.

Keep reading to find out more about why you might sometimes get the Reader’s Digest version of your period.

When it comes to menstrual cycles, there’s no single definition of “normal.” You can even have two periods in a single month! Instead of considering specific numbers to be normal (i.e., a 28-day cycle with a 5-day period), think of ranges instead.

What’s normal for one person’s period might not be for another — and that can change throughout your lifetime. The average menstrual cycle is about 28 days, but yours is considered “regular” if it’s between 21 and 45 days long.

Day 1 of your period is the first day you bleed; your next cycle starts the next time you bleed. And, if your period isn’t aligned with the moon and predictable down to the day and hour, you’re not the only one.

Between 5 and 35 percent of periods are irregular — let’s call them “free-spirited” — and vary in length and duration from month to month.

Bleeding for 5 days is the average, but anything from 2 to 8 days is within the normal range.

If a 2-day period is still within the normal range, what does that mean if yours is only 1 day — especially if you usually bleed for several days out of the month? Is it a gift from the universe? Is it too early to be your real period? Or is something else going on in your body?

Sometimes a 1-day period is also a super-light period (think: a pantyliner or free bleed kind of day). And other times, it’s a full-on Red Wedding re-enactment, like your body is trying to condense your usual period into 24 hours.

Here’s a look at some different reasons for 1-day periods, and what you might experience.

Pregnancy

When is a period not really a period? When you’re pregnant!

A short, light “period” of 1 to 2 days might be implantation bleeding, which is common. This happens about a week or 2 after fertilization in 15 to 25 percent of pregnancies, according to the American College of Obstetricians and Gynecologists.

You might also experience spotting early on because the blood vessels in your cervix are developing and thus more prone to bleeding.

Miscarriage

Bleeding from a miscarriage can also be mistaken for a short period, especially if you are not aware that you’re pregnant. Bleeding can range from light spotting to heavy flow, depending on how far along the pregnancy is.

You might also experience cramps or pain in your abdomen and/or back. Contact your doctor if you suspect you’re experiencing a miscarriage.

Ectopic pregnancy

Ectopic pregnancy (also called a tubal pregnancy) happens when a fertilized egg implants itself somewhere other than the uterus, such as in a fallopian tube, the cervix, or an ovary. If the egg continues to grow, it can rupture the tube, which can cause heavy internal bleeding.

Vaginal bleeding and pelvic pain are early symptoms of this serious condition, so seek medical attention immediately if you experience these or more severe symptoms:

  • abnormal bleeding
  • dizziness or fainting
  • pressure in your rectum
  • severe pain in your abdomen or pelvis, especially on one side

Breastfeeding

A short, light period can also happen while you’re breastfeeding. You usually don’t get your period when you’re breastfeeding, due to the hormone prolactin, which promotes lactation and tells your body not to have a period.

It will eventually come back though, usually about 9 to 18 months after your baby is born.

The pill and other medications

Hormonal birth control pills and shots can definitely cause your period to be both shorter and lighter, since they contain hormones that can thin the lining of your uterus. A thinner lining equals less to shed each month and thus a less intense period.

Intrauterine devices (IUDs) can cause the same.

Other medications — including prescription drugs, over-the-counter medicine and supplements — can also lead to changes in your menstrual bleeding.

These include:

  • aspirin and prescription blood thinners
  • nonsteroidal anti-inflammatory drugs (NSAIDs) and naproxen
  • hormonal therapy drugs (such as estrogen or progesterone)
  • medicines to treat cancer
  • thyroid medications
  • some antidepressants
  • herbal supplements that affect bleeding, including turmeric, ginger, ginkgo biloba, and ginseng

If you take any of these medications and experience a change in your usual menstrual flow, talk to your doctor.

Your lifestyle

What’s new with you lately? Any changes in your daily routine? Shifts in your diet, workout regimen or stress levels can all impact your period.

Major weight loss

Losing too much weight too quickly can affect your period. Weight loss, as well as eating disorders like anorexia nervosa and bulimia nervosa, can cause irregular and even skipped periods.

This is a sign that your body is not getting the nourishment it needs to maintain your menstrual health and other reproductive functions.

Stress

Seriously, is there anything stress doesn’t impact? (Short answer: Nope!) Stress can wreak havoc on your hormones, and when it’s severe enough, it might lead to a shorter, lighter, or a less regular period. (Thus compounding your stress!) It can also cause you to skip periods.

Your period is a barometer for your stress level. Once your stress goes down to a manageable level, your cycle likely will even out, too.

Too much exercise

Excessive physical activity can lead to irregular or missed periods. If you’re an endurance athlete, are training for a competition, or have recently changed your exercise level without adjusting your food intake, your body might not have the energy it needs for healthy menstruation.

Medical conditions

Certain medical conditions could also be the reason for your 1-day period.

Thyroid disease

Thyroid hormones are crucial to your menstrual health, so when thyroid disease causes your body to make too much or not enough of those hormones, it can impact your cycle. Your periods might be irregular or shorter when you have a thyroid issue.

Symptoms of thyroid disease vary by type but include:

  • feeling super tired or struggling to fall sleep
  • a heart rate that’s slower or faster than normal
  • gaining weight or losing weight unexpectedly

Polycystic ovary syndrome (PCOS)

PCOS causes your body to overproduce male hormones, and that imbalance can suppress ovulation and disrupt your cycle.

In addition to symptoms like fatigue, a low voice, mood swings, excess facial hair, and infertility, PCOS can also cause your periods to be lighter and shorter. You might even skip them altogether.

Other health conditions

These issues can also impact your period:

  • anemia
  • conditions involving the uterus, cervix, or ovaries
  • uterine or cervical cancer
  • disorders of the pituitary gland

Age

The most common age to start your period is 12 to 13 (earlier or later is normal, too), while the average age for menopause is 51. That’s almost 4 decades of menstruation!

It’s quite common for your periods to be irregular during those first few years as well as during the last few years (the perimenopause phase).

tl;dr

  • 1-day periods happen for a variety of reasons, from pregnancy and breastfeeding to medications and lifestyle changes.
  • One day of bleeding is not necessarily cause for alarm.
  • A “normal” period is what’s normal for you. Regular periods last 2 to 8 days, and regular cycles are between 21 and 45 days long.
  • If your period is suddenly cut short, make an appointment with your healthcare provider to figure out what’s causing the change.