Most women jump right to wondering if they’re pregnant when their menstrual period is late, but there are many reasons why ol’ Aunt Flo is running behind schedule…or not showing up at all. Sure, pregnancy is one of the biggest ones—it’s just not the only one.
The normal menstrual cycle is a tightly coordinated cycle of stimulatory and inhibitory effects that results in the release of a single mature egg from one of the ovaries. Your age and reproductive history, your hormones, your overall health, and even your lifestyle (aka stress, illness, sleep, and so on) all impact the timing of your period.
How late can a period be?
According to the Cleveland Clinic, the average length of a woman’s menstrual cycle is 28 days. Cycle length is counted as the first day of menstrual bleeding to the first day of menstrual bleeding. Note that we said average: Many women have shorter and longer cycles that still fall within the range of normal.
In fact, your menstrual cycle can last anywhere from 21 to 35 days without raising any eyebrows. Cycles that last longer than 35 days can be a sign of menstrual irregularities, like oligomenorrhea or polymenorrhea, but can also simply mean that your body is more sensitive to things like changes in sleep patterns or excessive stress. Being new to menstruation, breastfeeding, being postpartum, and transitioning to menopause also affect the length of your cycle.
So, what actually constitutes a “late” period? Opinions vary, but in general, your period is considered late if it’s five days past due per your routine cycle length, or is considered missed entirely (amenorrhea) if it’s been six weeks or more since your last period.
Since normal menstrual cycles can vary in length from woman to woman and even among the same woman at different times in her life (i.e., sometimes your cycle is 26 days and sometimes it’s 30), it is hard to get a reliable picture. The easiest way to calculate the length of your menstrual cycle is by tracking it for a couple of months and average the cycle lengths: Write down when your period begins each time you get it, for three to four months in a row, then add up the total number of days included in your tracking and divide by however many months you tracked for.
For example, if you tracked your cycle for three months, with the first period you recorded occurring 93 days before the start of your most recent period, you would divide 93 by three to get an average cycle length of 31 days. If you don’t want to do these calculations yourself, you can also download a period tracking app to your smartphone or tablet and let it do all the work for you.
Why is my period late? 11 reasons other than pregnancy
Of course, check a pregnancy test first. The over-the-counter urine-stick pregnancy tests are very accurate and inexpensive. If you’re definitely not pregnant, here are 11 other reasons for a late period:
- Contraceptives
- Perimenopause
- Weight changes
- Hormonal imbalances
- Stress
- Chronic illness
- Breastfeeding
- Medications
- Endometriosis
- Ovarian cysts
- Alcohol and tobacco use
1. Contraceptives
This might seem counterintuitive (aren’t birth control pills supposed to regulate your cycle?), but hormonal contraceptives such as continuous dose estrogen/progesterone pills, the Depo-Provera shot, the birth control implant, and certain intrauterine devices (IUDs) can cause your period to not occur “on time,” according to Ella Speichinger, MD, an OB-GYN at University of Missouri Health Care.
Many women using these forms of birth control experience less days of bleeding per cycle and less bleeding overall. Per Tufts Medical Center, periods may even stop after about one year with use of a progesterone-only IUD, the implant, or the shot. Switching forms of birth control can also throw off your cycles.
2. Perimenopause
Whether your transition into menopause is happening prematurely or right when you expected it to, says Dr. Speichinger, it can disrupt your cycles. The perimenopausal years occur after the reproductive years, but before menopause. It is characterized by irregular menstrual cycles, endocrine changes, and often has accompanying symptoms such as hot flashes. Many women experience shorter or longer periods of time between menstruation during perimenopause, thanks to the uneven rising and falling of estrogen levels as your body goes through this hormonal change. The menopausal transition (or perimenopause) begins, on average, four years before the final menstrual period.
3. Weight changes
Weight gain or weight loss, especially quickly or suddenly, often disrupts menstrual cycles. An increase in body fat is associated with an excess amount of estrogen, which needs to be well-balanced in order to have a regular period schedule.
Similarly, losing a lot of weight or becoming underweight (BMI less than 20) can delay periods as well, particularly in the context of any disordered eating. The NHS reports that severe calorie restriction, such as with anorexia, bulimia, or similar eating disorders, sends a message to your brain to stop producing the hormones needed for ovulation (and if you don’t ovulate, you won’t have a “true” period, though you may still experience some vaginal bleeding).
4. Hormonal imbalances
According to Dr. Speichinger, hormonal imbalances can be caused by a number of different health conditions: thyroid disease like hyperthyroidism or hypothyroidism, polycystic ovary syndrome (PCOS), primary ovarian insufficiency, and hyperprolactinemia, or having too much of a hormone called prolactin in your blood.
It is crucial to reproductive health that female hormones are correctly balanced; with all of these medical conditions, the relationship between various hormones such as estrogen, progesterone, prolactin, and even testosterone can be thrown out of sync. When this happens, you might experience irregular or missed periods, along with other symptoms like infertility and non-menstrual uterine bleeding. Talk to a healthcare provider about ordering blood tests to get a more accurate picture of your hormone levels.
5. Stress
Being excessively stressed or stressed for a long time can interrupt your regular menstrual cycle thanks to another hormone our bodies make more of in times of stress: cortisol. According to the Mayo Clinic, the production of cortisol can affect the signals sent to your ovaries when it’s time to release an egg, delaying ovulation and, by default, your period.
6. Chronic illness
Chronic illness or even one particularly severe acute illness can also interfere with your cycle. Our bodies can become stressed when we’re ill, responding to a bad virus or bout of strep throat the same way they would if we experienced a death in the family (i.e., too much cortisol, not enough ovulation-inducing hormones). Chronic illness, like diabetes, can also interfere, partly because diabetes is associated with higher rates of obesity and PCOS, which are both factors causing irregular periods.
7. Breastfeeding
After giving birth, it often takes several months to get a period again, and even longer before your periods become normal. Dr. Speichinger notes the time between giving birth and your first period can be anywhere from three to six months.
It may be shorter if you don’t breastfeed, or longer if you breastfeed exclusively. Per the NHS, the hormones that help you lactate also reduce the amount of menstruation hormones. Since most babies are introduced to some solid foods after six months, even exclusively-breastfeeding women may see a return of their periods around that time, though sometimes it takes until the baby is fully weaned for their periods or for ovulation to return. However, just because you are breastfeeding doesn’t mean you can’t still get pregnant. Be sure to use birth control if you’re sexually active: condoms and progesterone-only forms of contraceptives are helpful in the breastfeeding mother.
8. Medications
Samara Gibson, MD, an OB-GYN at Detroit Medical Center, says that in addition to hormonal birth control, other drugs such as psychiatric medications are a common cause of period changes.
According to a 2013 review in Schizophrenia Research and Treatment, both typical and atypical antipsychotics can cause late or missed periods, with an increase in prolactin believed to be the primary reason. Other drugs that affect hormones, like thyroid medications and even steroids, can cause delays, too.
And it’s not just prescription drugs that can disrupt your flow: “Supplements that you can find at health food stores can also change your cycles,” Dr. Gibson says.
In general, however, this relates to the misuse of supplements; there’s not much evidence that vitamins, especially a daily women’s vitamin, can interfere with your cycle unless you’re taking an inappropriate amount. (In fact, some researchers have linked vitamin D supplementation to an improvement in delayed or missed periods.)
RELATED: How much vitamin D should I take?
9. Endometriosis
Endometriosis, a condition where endometrial (uterine lining) tissue grows outside the uterus, often causes irregular periods or longer periods. In other words, your cycle may not arrive on schedule, and vaginal bleeding may last more than the typical five to seven days. That’s because your body has excess lining to shed. Spotting in between periods is also common for women with endometriosis.
RELATED: Endometriosis treatments and medications
10. Ovarian cysts
Similar to endometriosis, ovarian cysts can lead to heavy, irregular periods, and spotting in between periods. Certain types of cysts produce hormones that can mess with your monthly cycle. Most cysts will resolve on their own. Check with your healthcare provider for diagnosis and treatment options.
11. Alcohol and tobacco use
Both cigarette smoking and excessive alcohol use have been linked to disruptions in menstrual cycles. Why? These substances may affect hormone production, which can throw off your monthly menses.
What happens to your body if you skip a period?
According to Dr. Speichinger, missing one period isn’t dangerous, but if you go more than three months without a period or continue to miss periods intermittently over a long period of time, there is the potential for problems depending on the reason why it’s happening. Some hormonal imbalances can affect the health of the uterus over time.
“If the lack of a period is due to too much estrogen compared to other hormones, as is the case with PCOS or excess weight, then there is the added risk of having abnormal cells develop in the uterus,” Dr. Speichinger explains.
If you don’t know the reason for your menstrual irregularities or missed periods, it’s a good idea to check in with your provider. “Notify your doctor at your annual examinations if your cycle is [frequently] irregular,” Dr. Gibson says. “If you miss a cycle, take a pregnancy test, [and] if you miss more than two periods, contact your doctor.”
How to induce your period
Whether or not you can jump start your period or encourage it to happen depends on the root cause of the delay. In the long-term, Dr. Speichinger says that addressing some of the issues that can cause late or missed periods can help get your cycle back on track. Reducing your stress levels, getting adequate rest, cutting back on excessive exercise if you’re an athlete, and normalizing your weight can reset your cycle if those things have caused the disruption in the first place.
There are also medication options that may be available to you, especially if your late period is because of a hormone imbalance. “Typically, we can start with a progesterone challenge to [induce] a withdrawal period,” Dr. Speichinger explains.
A progesterone challenge test involves taking progesterone orally for about 10 days, then stopping the progesterone to see if withdrawal bleeding occurs. If it does, there may be an issue with ovulation; if it doesn’t, the problem may be related to estrogen levels. Dr. Speichinger notes that sometimes there is a second step to the progesterone challenge, where estrogen is given first and followed by progesterone, to cause the withdrawal period.
RELATED: Understanding low progesterone levels
This test can tell your women’s health provider a lot about your hormonal levels, as well as the health of the lining of your uterus. It can make the next steps clearer for you and your provider as you look for the source of your late or missed periods.
