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The menstrual cycle is the time from the first day of your period (the day you start bleeding) until the day before your next period starts.

It’s important to know your own unique cycle so you can learn what’s normal for you. Cycles aren’t the same for everyone. Cycles can range anywhere from 21 to 35 days, and periods (the time you’re bleeding) can last anywhere from 2 to 7 days. 

Knowing your own cycle can help you figure out when you ovulate, which is when you're most likely to get pregnant. It also helps you notice any changes like missing a period, having unexpected bleeding, or having more pain than usual. Sometimes, changes in your menstrual cycle can be a sign of health issues.

Find an overview of the menstrual cycle and what happens during each stage of the cycle on our menstrual cycle page.

Talk to your medical provider if you have any concerns about your menstrual cycle. Here are some reasons you should talk to your doctor:

• Your periods suddenly stop for more than 90 days and you know you’re not pregnant.
• Your periods become irregular after having been regular.
• You bleed for more than seven days.
• You bleed more than usual or soak through more than one pad or tampon every hour.
• Your periods are less than 21 days or more than 35 days apart.
• You bleed between periods.
• You have severe pain during your period.
• You suddenly get a fever and feel sick after using tampons or menstrual cups.

Note: Some types of hormonal birth control can cause changes to your menstrual cycle. Talk to your provider about what you can expect with the birth control method you choose. 

When can I get pregnant?

When you ovulate you are fertile and can become pregnant. Ovulation usually happens 10 days to 3 weeks after the first day of your period. This window of fertility usually lasts about 5 to 6 days per cycle. Using an ovulation calculator may be helpful. Sperm can survive for several days inside the female reproductive system, so consider that as well. 

Learn more about what your chances of getting pregnant really are.

Toxic shock syndrome

It’s important to also talk about toxic shock syndrome (TSS) when you talk about periods. TSS is a rare but serious complication that results from an infection.

TSS has many causes, but one common cause is keeping tampons and menstrual cups in the vagina for too long.

When you use these items, don't keep them in the vagina for longer than needed. Follow the guidance on the package for each individual product.

When you use tampons, use the lowest absorbency tampon you can that will manage your flow, and don't keep a tampon in for more than 8 hours without changing to a new one.

Some symptoms of TSS include:

• Sudden high fever, chills, body aches, or other flu-like symptoms
• Nausea or vomiting
• Rash
• Dizziness, lightheadedness, or fainting

If you have any of these symptoms or suspect TSS, seek medical care right away.