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What’s “normal”?: menstrual cycle length and variation

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Top things to know:

  • The length of your cycle is the number of days between periods, counting the first day of your period until the day before your next period starts

  • For adults not using any form of hormonal contraceptive or IUD, a typical cycle length ranges between 24 to 38 days

  • Using hormonal birth control or an IUD may change the length and variation of your cycle

The menstrual cycle is more than just your period—it’s the rhythmic changes of the your reproductive system. The changes throughout the menstrual cycle are governed by hormones, which include estrogen, progesterone, follicle stimulating hormone, testosterone and others. They trigger the growth of follicles in the ovaries, the release of an egg (ovulation), and the growth and shedding of the uterine lining (the period).

Having a menstrual cycle is like having an additional vital sign, like your blood pressure or your pulse (1). Your cycle can let you know when everything is working as usual, when your body is going through a change, or when something’s not as it should be. Some variation in your cycle is completely normal, but a cycle that is consistently out-of-range may be the first noticeable symptom of a treatable health condition.

What is a normal cycle length for people not on hormonal birth control?

Adult cycle length

A normal menstrual cycle length for an adult who is not using any form of hormonal contraceptive or IUD usually is between 24 to 38 days (2). This means that an adult will have between 11 to 13 menstrual cycles per year (2).

Variations of cycle lengths are normal (3). Within the same year, the length between the longest cycle and the shortest cycle can vary up to 9 days and still be considered within normal ranges. For example, a normal variation can be that one cycle is 25 days long, followed by a cycle that is 33 days long (4).

The majority of your cycles should fall within this range, but it’s normal to have some cycles be longer or shorter. The length of your cycle can be affected by factors like stress, diet, jet lag, or exercise—anything that affects your reproductive hormones (5-11).

Adolescent cycle length

The menstrual cycles of adolescents around the time of menarche (the first menstrual period) can vary greatly (12). It’s common for cycles to be somewhat irregular for a few years after your first period (13). This means your periods may not always come at the same time every cycle, and they may be somewhat different cycle-to-cycle. As you progress through adolescence, cycles become more regular to reflect adult cycle ranges, but may still be somewhat variable (12-14).

A normal menstrual cycle length for an adolescent usually is between 21 to 45 days, but may sometimes be longer or shorter (14).

At the onset of menarche, you may not ovulate with every cycle. However, as you progress through puberty, ovulation will likely happen in most of your cycles, which will help regulate your cycle length (12). Anovulatory cycles (a menstrual cycle in which an egg is not released from an ovaries) may make cycle lengths irregular and longer (1).

What is a normal cycle length for people on hormonal birth control (e.g. the pill, the ring, the patch)?

Hormonal birth control (HBC)—like the pill, the vaginal ring, or the patch—control the regulation of hormones like estrogen and progesterone within your body (15). When used correctly, the hormones in your HBC prevent your ovaries from preparing and releasing eggs. This stops your body’s usual hormonal cycling rhythm, allowing the HBC to control of the growth and shedding of your uterine lining (your period).

Your cycle length will depend on the type of HBC you use.

The pill

The birth control pill is commonly dosed in packs which provide a 28-day cycle, with 21 to 24 days containing active hormones, and four to seven days containing pills with no hormones or not taking any pills during those days (16). Bleeding will happen during these “no-hormone” days, due to the withdrawal of hormones. This will make your cycle regular and be approximately 28 days every cycle (15). When you first start taking the pill or if you take your pills inconsistently, you may experience spotting or breakthrough bleeding (15,16).

Continuous cycle pill packages also exist, with 90-day pill packs, or 365-day pill packs (15). These will make your cycle 3 months or a year long.

The ring and the patch

The vaginal ring and patch are often dosed across a four week cycle (15). The vaginal ring contains both estrogen and progesterone and is inserted into the vagina for 21 days and then removed for seven days, which then stimulates bleeding (15). The contraceptive patch is also used on a four-week schedule, with a new patch being applied for three weeks in a row, followed by one week of “no-patch” which stimulates withdrawal bleeding. Both of these methods will make your cycle regular and approximately 28 days long when used correctly (15).

Some people also decide to skip any bleeding while using HBC, by skipping over the “no-hormone” days. This will extend your cycle length until the end of your next pack of birth control pills or when you remove your ring or patch. Breakthrough bleeding or spotting is common with extended use (17).

What is a normal cycle length for people on progestin-only birth control (e.g. the mini pill, the shot, the implant)?

There are many different types of hormonal birth control, all containing differing types and levels of hormones. Some types of birth control do not contain any estrogens and only contain progestin—a synthetic form of progesterone (16). These methods include progestin-only pills (the mini pill), progestin injections (the shot), or progestin implants (16,18).

The mini pill

When using progestin-only birth control pills, you may not have a typical menstrual cycle. Progestin-only HBC pills affects reproductive hormonal cycling by often preventing the ovaries from preparing and releasing eggs (18,19). They also decrease and thin out the typical growth of the uterine lining. Many people experience irregular bleeding, reduced bleeding, shorter cycles, or amenorrhea (no menstrual period) with progestin-only pills, especially when pills are not taken at the same time every day (18).

The shot and the implant

The injection and the implant both work to stop ovulation, which prevents hormone cycling (18,20). Both of these contraception methods often impact menstrual cycles by either prolonging or shortening cycle lengths (18,20). Many people, particularly those who are using the contraceptive shot, over time will even experience amenorrhea (18,20,21). Many people experience unpredictable bleeding or spotting, though the frequency of bleeding days decreases over time (18,20-24). All of these changes are normal with these forms of birth control.

Intrauterine devices (IUDs) and your cycle

Cycle length and the hormonal intrauterine device (IUD)

When using a hormonal IUD, you may not have a typical cycle. Your cycle length and period may change depending upon which hormonal IUD you have and how long you’ve had it. IUDs with a lower progestin dose are less likely to suppress ovulation in comparison to IUDs with higher doses of progestin (25,26).

Cycles may be longer, or the same as before your IUD. Periods often get lighter and many people stop having their periods completely with the hormonal IUD (16). It’s also common to have light, irregular spotting, especially in the first few months (16). Your cycle length is also likely to change over time on the hormonal IUD (16).

Cycle length and the copper IUD

Having a copper IUD shouldn’t affect your cycle length since copper IUDs are non-hormonal, so you will experience the same fluctuations of estrogen and progesterone across your cycle as you did when you weren’t using a copper IUD (27). That means the majority of your cycles should be 24–38 days long, which is the normal range for cycle length in adults. Some people using a copper IUD may notice that your period is heavier and longer, or they may experience unscheduled spotting, but these side effects often improve over time (16,28).

Irregular cycles while using hormonal birth control

It’s not uncommon to have light spotting when you’ve just started using hormonal birth control or when you’ve recently switched to a new hormonal birth control. If you’ve been using your HBC for over three months and are still having common breakthrough bleeding, you might talk to your healthcare provider about switching your type or brand of HBC. Spotting can also occur if you have chosen not to skip your period while using HBC (17).

Using your HBC inconsistently or incorrectly can cause irregular bleeding. This will affect the length of your cycle and the heaviness of your period. People who use HBC incorrectly are also at an increased risk of pregnancy compared to people who use HBC correctly. Forgetting to take your HBC pills, taking placebo pills early, or removing a ring or patch early can increase pregnancy risk.

Why cycles vary

The length of your typical cycle is determined by your age, genes, health, body mass index (BMI), behaviors, and birth control methods (16,29).

If you’ve had your period for a few years, your cycle should generally be about the same length each cycle. You may still notice changes from time to time—?the length of your cycle depends on your hormones, which can fluctuate due to factors like diet, stress, shift work, or taking an emergency contraception pill (the morning-after pill) (5-11,30).

Menstrual cycles can fluctuate when ovulation doesn’t occur. This is one reason why cycles vary greatly during adolescence, after giving birth, during breastfeeding, and during perimenopause (the menopausal transition) (31,32). People are less likely to ovulate consistently during these times.

Exercise, smoking cigarettes, and drinking alcohol may also affect cycle length and variation (33-38).

Download Clue to track your menstrual cycle length.

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