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Menstrual Irregularities: Top 10 Reasons Your Period is Late, Early, or Missing

Generally speaking, menstrual irregularities are only cause for concern when they happen often. But you may still be wondering why your period is irregular, especially if you’re avoiding pregnancy.

For peace of mind, know that many factors can cause late, early or irregular periods. This article explains what they are and why they disturb your cycle.

Key things to understand about menstrual irregularities:
  • The timing of your period depends on the timing of ovulation. Unless you’re pregnant, a delayed or missing period means you didn’t ovulate that cycle, or ovulated late.
  • Ovulation is finicky. It won’t happen unless the right hormones are produced in the right amounts, and a number of stressors can throw it out of whack.
  • In most causes, irregular periods are temporary. If your cycle doesn’t return to normal when the stressor subsides, tell your doctor.
  • Ovulating consistently is how you have regular menstrual cycles. We discuss how to support healthy ovulation every cycle.

Why your period is irregular

All menstrual irregularities start with ovulation—the mid-cycle release of an egg from your ovary. Or rather, they start with the lack thereof.

When you ovulate, one of two events will happen: you will either become pregnant, or you will have a period about 2 weeks later. Those are the only options.

If your period is missing, it means you either are pregnant, or you didn’t ovulate when you normally do.

If you’re sexually active, rule out pregnancy by taking a pregnancy test—especially if your period is usually regular. But if you’re using reliable contraception, it’s more likely that you haven’t ovulated. One study tracked the ovulatory pattern of 550 women, and found over 25% experienced anovulatory cycles, meaning ovulation didn’t occur at its usual time. (1)

Anovulatory cycles still involve bleeding, but it’s not technically a period, as only ovulation can trigger your ‘true’ period. Anovulatory bleeds may arrive early or late, and be heavier than usual.

It’s also possible to ovulate in a given cycle, but do it much later than you usually do. Your period may feel similar to how it normally feels, it will just arrive days or weeks late.

Things that can cause irregular periods

A number of factors can cause menstrual irregularities by throwing off ovulation timing. They include:

  • Physical or emotional stress
  • Weight changes
  • Exercising too much
  • Illness or medical condition
  • Medication changes
  • Too little sleep
  • Perimenopause
  • Recently started menstruating
  • Recently stopped using hormonal birth control
  • Recently vaccinated from COVID-19

It’s normal to have an irregular cycle every once in a while, even if you’re healthy. See a healthcare practitioner if you experience irregular periods often, especially if they come with severe cramps or PMS symptoms.

Learn more about how to know if you’ve ovulated here.


10 possible causes for menstrual irregularities


Menstruation is considered a vital sign of health, which means regular, manageable periods are your body’s way of telling your system is working like it should be. (2)

Stress signals to your body that it's a bad time for pregnancy. Ovulation will shut down (thus delaying your period) until you’re better able to support a potential fetus. Even if you don’t want to become pregnant, your biological ability to do so is important to your overall health.

Mental health and menstrual health are strongly linked. Major life changes like moving, breakups, job changes, or traumatic events can all affect your cycle. Losing your period altogether (also known as amenorrhea) is the most severe form of stress-induced menstrual disturbance.


Fat tissue is an endocrine organ (3), which means it helps hormones stay in balance. When we lose or gain enough of it too quickly, our hormones respond, and may need time to adjust.

While both weight gains and losses can cause hormonal disturbances, weight loss is more likely to negatively affect your cycle. Ovulation thrives on hearty starches and lean proteins for lasting energy; undereating often means your cycle isn’t getting the nutrition it needs. Note that it’s possible to undereat without experiencing weight changes.


Too much physical activity can cause menstrual irregularities because your body diverts energy and resources away from ovulation, and toward fueling your workout instead. If you’re experiencing irregular or missing periods after leveling up your exercise regimen, take it as a sign you’re pushing yourself too hard.


Being ill, whether it’s a passing infection or a chronic condition, is a type of physical stress that can cause your body to shut down non-essential functions like ovulation while it focuses on healing. If your period doesn’t return after you’ve recovered, talk to your doctor.


Starting, stopping, or changing the dose of your medication can cause irregular periods. This is especially true for drugs like antidepressants, blood pressure pills, or antibiotics. Always ask your doctor or pharmacist about all potential side effects of your meds.


Circadian rhythm (also known as the ‘sleep-wake’ cycle) is the body’s internal clock. Besides controlling how rested or fatigued you feel, it also controls the production of hormones that guide the ebbs and flows of your menstrual cycle.

While easier said than done, getting at least 7 hours of quality sleep each night can work wonders for your body’s internal cycles. Research shows that women working night shifts are more likely to experience irregular cycles and longer periods. (4)


Perimenopause refers to the time leading up to menopause, when the menstrual cycle naturally stops altogether. Perimenopause typically starts in a person’s 40s, but can begin as early as your mid-30s.

Menstrual irregularity is common during perimenopause as ovulation grows more unpredictable. Periods may arrive earlier or later, and may be heavier or lighter than they used to be. You may be experiencing early stages of perimenopause if your cycle is consistently 7 days longer or shorter than what was typical for you.


It’s normal to have irregular menstrual cycles if you got your first period within the last few years. Cycles often need time to establish their hormonal rhythms before they’re able to ovulate around the same time every month. It’s common to skip periods or get them more than a month apart when you’re new to menstruating. They usually become more regular with time.


Hormonal birth control (i.e. birth control pills, patches, injections, and IUDs) prevent pregnancy by shutting down ovulation. When you stop taking the pill or get your IUD removed, your system may need some time to relearn how to make its own reproductive hormones before it’s able to ovulate consistently again and bring you regular periods.

While some people ovulate right away after coming off the pill, it can take months (sometimes years) for others, especially if you were on the pill for a long time.


People have been reporting menstrual changes after receiving the Pfizer, Moderna, and Johnson & Johnson vaccines. Here’s everything you need to know.



Healthy ovulation is how you have regular periods

Irregular periods and PMS have something in common: lack of consistent ovulation (and the hormonal imbalances that follow) is the root cause for both. Conveniently, supporting healthy ovulation is also the solution for both.

We formulated Steady Mood—our daily multivitamin for multi-symptom PMS relief—with the most-researched natural ingredients for PMS relief, hormonal resilience, and stress management.

Steady Mood supports all phases of your menstrual cycle (including ovulation) with nutrients and herbs hormones need to thrive. Because the better you’re able to support your body through ovulation, the easier periods become. (5)



1. Malcolm, C. E., & Cumming, D. C. (2003). Does anovulation exist in eumenorrheic women?. Obstetrics & Gynecology, 102(2), 317-318.

2. American Academy of Pediatrics, & American College of Obstetricians and Gynecologists. (2006). Menstruation in girls and adolescents: using the menstrual cycle as a vital sign. Pediatrics, 118(5), 2245-2250.

3. Kershaw, E. E., & Flier, J. S. (2004). Adipose tissue as an endocrine organ. The Journal of Clinical Endocrinology & Metabolism, 89(6), 2548-2556.

4. Wang, Y., Gu, F., Deng, M., Guo, L., Lu, C., Zhou, C., ... & Xu, Y. (2016). Rotating shift work and menstrual characteristics in a cohort of Chinese nurses. BMC women's health, 16(1), 1-9.

5. Rapkin, A. J., Morgan, M., Goldman, L., Brann, D. W., Simone, D., & Mahesh, V. B. (1997). Progesterone metabolite allopregnanolone in women with premenstrual syndrome. Obstetrics & Gynecology, 90(5), 709-714.

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