Your period may come early due to changes in your hormone levels. This can occur due to puberty, perimenopause, certain medications, stress, or various health conditions.

Everyone’s menstrual cycle is different. Your cycle starts on the first day of your current period and ends on the first day of your next period.

A typical cycle lasts anywhere from 21 to 35 days, so the number of days spent bleeding varies from person to person. Most people bleed for two to seven days.

If your cycle is frequently shorter than 21 days — leading you to bleed earlier than you normally do — it could be a sign of something underlying.

Read on to learn which symptoms to watch for and when to see your doctor.

Puberty typically starts between ages eight and 13. It’s driven by chemicals in your body called reproductive hormones. These hormones will continue to affect your menstrual cycle throughout your child-bearing years.

In the first few years after you get your period, these hormones can be irregular. This means that the number of days between your periods may be shorter or longer than average.

Perimenopause is the transition into menopause. It typically begins in your mid to late forties and lasts about four years.

Your hormone levels fluctuate wildly during this time, and you may not ovulate every month. This can cause irregular periods, so you may menstruate sooner or later than usual.

Intense exercise can cause irregular periods or cause your period to stop altogether. Often, this condition is associated with athletes who train for several hours daily.

Exercise only affects your periods when you burn way more calories than you eat. Without adequate energy, your body doesn’t produce the amount of reproductive hormones it needs to ovulate normally.

Early, irregular, or missed periods are often associated with major weight changes.

Research shows that obesity in adolescence is associated with a higher chance of irregular periods.

Other research confirms this and also suggests that significant weight loss can lead to the same result. This can happen with extreme dieting, gastric bypass surgery, or eating disorders.

Severe stress also can disrupt your hormone levels, causing irregular periods. If you experience anxiety or have recently been through a traumatic event, this may throw your hormones out of whack.

Research suggests that people who switch between day and night shifts, like nurses, often experience irregular periods. Switching time zones may have similar effects.

Researchers believe this may be related to a disruption in your circadian rhythm. This may, in turn, disrupt the sleep hormone melatonin.

More research is needed to explore the connection between melatonin and reproductive hormones.

Taking blood thinners (anticoagulants) may prolong your period and cause heavy bleeding.

Anticoagulants are released naturally during your period to help thin the lining of your uterus, so it can flow out of the vagina. Taking anticoagulants may cause this process to happen faster and result in a heavier flow.

The hormones present in hormonal birth control directly affect ovulation and menstruation.

If you’re taking birth control pills, the timing of your next period will depend on when during your cycle you start ut and whether you’re taking a week of placebos (reminder pills).

This also applies to emergency contraception (EC). If you use EC pills routinely, your period may become irregular.

Other hormonal birth control options, like intrauterine devices (IUDs) and the Depo-Provera shot, can cause menstrual irregularities for the first two or three months.

Learn more about how birth control methods can affect your period.

Polycystic Ovary Syndrome (PCOS) is a common condition caused by a hormonal imbalance. It affects 1 in 10 females of child-bearing age.

Many people don’t know they have PCOS until they have difficulty becoming pregnant. It can also cause irregular or missed periods.

Endometriosis occurs when endometrium-like tissue begins to grow outside the uterus in areas like the ovaries, abdomen, and bowel.

It affects around 11% of females in the United States between the ages of 15 and 44 and can cause unexpected bleeding.

When diabetes is undiagnosed or poorly managed, blood sugar levels are chronically higher than normal. Both type 1 and type 2 diabetes can cause irregular bleeding.

It’s thought that one in eight females will develop a thyroid condition in their lifetime.

Your individual symptoms will depend on whether your thyroid is underactive or overactive. In addition to early menstruation, you may experience periods that are light or heavier than usual.

What is considered an early period?

Every person’s menstrual cycle is different, and it may vary from month to month. If your period shows up occasionally slightly earlier than expected, it’s probably nothing to worry about. If your cycle is consistently shorter than 21 days, it’s a good idea to consult with your doctor in case there’s an underlying cause.

Could I be pregnant if my period came early?

It’s not likely that your period will come if you’ve already conceived. That said, you can experience implantation bleeding, which may look like a period.

What’s the difference between an early period and implantation symptoms?

Implantation occurs when a fertilized egg attaches to the lining of your uterus. It happens one to two weeks after conception.

Implantation doesn’t always cause symptoms. When symptoms do occur, they include light bleeding or cramping. Bleeding is typically lighter than a typical period and usually won’t require a tampon or pad.

What’s the difference between early period and miscarriage symptoms?

A miscarriage is the loss of a pregnancy. Most miscarriages take place during the first trimester.

It often happens before the person is aware of the pregnancy, so it can be difficult to differentiate between a particularly heavy period and a miscarriage.

A miscarriage may cause more cramping and back pain than a typical period.

Learn more about identifying a period vs a miscarriage.

An early period usually isn’t a sign of anything serious. But if you’re in severe pain or discomfort, you should see your doctor.

You should also seek immediate medical attention if you’ve experienced a miscarriage or suspect that you have.

If you aren’t experiencing any severe symptoms, you may be able to regulate things at home. Consider tracking your periods for the next two to three months to see how your timing, flow, and other symptoms compare.

If things aren’t leveling out, talk with your doctor. They can use this information to evaluate your cycle and advise you on any next steps.