Illustration by Emma Günther
Why is my menstrual cycle length changing?
Discover the possible reasons and when to see a healthcare provider
Top things to know about cycle length:
Menstrual cycles naturally vary, and a perfectly “regular” cycle is rare
Life stages, stress, birth control, and medical conditions can all affect cycle timing
Reproductive hormones play a key role in regulating cycle length and overall health
Tracking your cycle with Clue can help you understand changes and know when to seek medical advice
Why did my menstrual cycle change?
Menstrual cycles are dynamic and rarely follow the exact same pattern every time. No one’s cycle is perfectly “regular.” Your period is like an extra vital sign—just as your pulse or temperature can signal changes in your health, so can your cycle (1). Understanding your cycle’s length and its variations can help you notice when things are following your usual rhythm or when something might need a closer look (1).
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No one is perfectly “regular”
A period that lands on the exact same day each month is not the norm. In the years after you start menstruating, as you approach menopause, when you’re pregnant, or when you’re adjusting to a new contraceptive method, your cycle will naturally change (1-3). Even outside of those times, small changes in timing and cycle-related experiences are typical (4).
In one cycle, ovulation might occur a couple of days later than usual. Progesterone (the hormone that’s dominant after ovulation) will then peak later in your cycle (4). This causes premenstrual symptoms (such as sore breasts) to happen later as well. Your period will then also be a couple of days late (4).
If your period is late and there's a chance you could be pregnant, consider taking a pregnancy test. Some early signs of pregnancy, such as changes in breast tenderness or spotting, may occur before a missed period (5). If in doubt, testing on the first day of a missed period can provide more clarity.
Regular ranges: What’s “normal”?
Clinicians consider a cycle “regular” when most of your cycles and periods fall within these ranges:
Adolescents
Cycle length within 21–45 days (1)
Adults
Cycle length within 24–38 days (6)
Up to 7–9 days difference between your shortest and longest cycle (6)
Periods lasting 8 days or fewer (6)
A little mid-cycle spotting may be caused by ovulation (4). However, if you notice unpredictable spotting or your period length is changing continually, it might be a good idea to talk with your healthcare provider (6). If the majority of your cycles fall outside these ranges, check out our guide on what’s considered a “normal” menstrual cycle length and variation.
Why am I experiencing a change in my cycle length?
Menstrual cycles are caused by the rhythmic fluctuations of your reproductive hormones (4). These hormonal changes 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). Any shift in the balance of your reproductive hormones can change your cycle’s timing and the way you feel during your period.
Think of your hormones as runners in a relay race–each hormone triggers the next step. If one hormone’s signal is a bit off, the timing of your cycle can shift (7). Up next, we’ll break down some common factors that can change your cycle.
What can cause one-off or short-term changes in your cycle?
Sometimes, you might see more significant changes in your cycle. These can be temporary, lasting just one or two cycles, and might be linked to factors like high stress, not getting enough calories (8–10), or very early miscarriages (11). It’s also possible to miss ovulation in a cycle, which can result in a longer cycle with a lighter period (4).
Some of these short-term variations, like stress or a missed ovulation, are usually not a cause for concern. However, menstrual cycle irregularities can be longer-lasting. If your cycles consistently fall outside the “regular” ranges and the changes last for six months or more, it may be a sign of a longer-term issue (6,12).
Common factors that may cause your “regular” cycle to vary
Factors like working night shifts, intensive exercise, or medical conditions such as polycystic ovary syndrome (PCOS) can affect your cycle (9,10,13,14). It’s also possible that an undiagnosed medical condition could be the reason for menstrual cycle changes (11). Periods that are very heavy or painful may also signal an issue—endometriosis, for example, is a common (and underdiagnosed) cause of painful menstruation (15).
Reproductive hormones like estrogen play a role in more than just the menstrual cycle; they also influence your sleep, mood, weight, bone health, heart health, and more (16–20). So, if your cycle consistently feels “off,” this can sometimes reflect broader hormone changes that may affect overall health, and it’s a good idea to consult your healthcare provider.
Below, we break down some key factors that might make your cycle longer or shorter:
Life stages and pregnancy
After menarche (first period): When you first start menstruating, cycles can be more unpredictable (1).
Perimenopause: As you near menopause, your cycles may change (2).
Pregnancy and postpartum: Hormonal shifts during and after pregnancy—especially changes in estrogen levels—can affect your cycle (21,22).
Breastfeeding/ chest feeding: Lactation can suppress ovulation and alter cycle timing (21).
Miscarriage or abortion: These events can also lead to temporary changes (11,23).
Birth control and contraceptives
Changing or stopping hormonal birth control: Adjusting your birth control can shift your cycle’s timing (3).
Emergency contraceptive pills: These work by blocking or delaying ovulation, which can have an impact on cycle length and timing (3).
Sleep/wake cycles
Shift work or night shifts: Irregular sleep patterns can have an impact on your reproductive hormones and influence your cycle (13).
Travel and jet lag: Changing time zones may temporarily affect your reproductive hormones (13).
Physical and emotional changes
Stress: Higher stress levels are linked to menstrual changes (8,9).
Diet and exercise: Not getting enough calories, intensive exercising, and significant weight loss or gain can alter your cycle (10,24,25).
Substance use: Smoking, alcohol, and other substances have been linked to menstrual cycle disturbances, but more research is needed (26).
Conditions and medications
Polycystic ovary syndrome (PCOS): This is a common condition that can cause irregular cycles (14).
Thyroid disorders: Your thyroid plays a key role in regulating hormones and can affect your menstrual cycle (27).
Medications: Some medications, such as certain antidepressants and antipsychotics, have been linked to menstrual cycle changes (28,29).
When should I be worried about my cycle length?
While some variation is typical, there are times when you should reach out to a healthcare provider (12):
Consistent irregularities: If most of your cycles over the past six months fall outside the “regular” ranges listed above.
Severe symptoms: If you experience very heavy bleeding, severe pain, or other concerning symptoms.
Sudden, lasting changes: If your cycle changes abruptly and remains different over several cycles.
Your healthcare provider can help determine if further investigation or treatment is needed.
How to track and know your cycle
Understanding your average cycle is the first step to noticing changes. Tracking your cycle with Clue can help you identify patterns and understand how different factors—like stress, sleep, or diet—might be affecting you. This information not only gives you peace of mind but can also be valuable to your healthcare provider when making decisions about your reproductive health. It might even help you spot early changes related to menopause, breastfeeding, or pregnancy.
And if a cycle doesn ’t reflect your usual pattern—like after traveling or during a particularly stressful month—you can exclude it in Clue to keep your predictions accurate. Just tap the three dots in your cycle history and select “Hide this cycle.”
FAQs
Why did my cycle change from 28 to 31 days?
A slight change like this is common. Ovulation can vary from cycle to cycle, which may shift the length of your cycle by up to 9 days (4,6).
Could a change in cycle length be a sign of menopause approaching?
While changes in your cycle may be a sign of the transition towards menopause, they can also be part of your typical cycle variation (2). Learn more about the signs of perimenopause in our perimenopause 101 article.
