Why is my period late? 13 possible reasons behind your delayed period

If your period doesn’t show up on time and you’re not trying to conceive, it’s natural to feel concerned. But a late period doesn’t necessarily mean that you’re pregnant or that anything is seriously wrong. 

Here are 12 of the most common reasons for a late menstrual cycle to help you figure out why your period might be late (or even a no-show) this month. 

Key takeaways 

• Lifestyle changes like stress, significant changes in diet, and extreme exercise can be reasons for a late period.
• Certain medications and health conditions like polycystic ovary syndrome (PCOS) can also cause irregular cycles and a late or missed period.
• Pregnancy can also cause a missed period.
• It’s normal for your menstrual cycle to vary slightly each month, but if your cycle length varies by over seven to nine days, then it’s considered irregular. 
• Always speak to your doctor if you’re concerned about a late or missed period.

Understanding the menstrual cycle

Although a late period can be confusing, having an understanding of the menstrual cycle and the body can help clarify this situation. So let’s have a quick refresh on how the menstrual cycle works.

Each menstrual cycle begins on the first day of your period and continues until the next period begins. The average cycle length is about 28 days long, but a healthy cycle can be anywhere from 21 to 35 days long. (Interestingly, a large study conducted by Flo and the University of Adelaide showed that only about 16% of the participants had a 28-day cycle, even though it’s considered the typical length for menstrual cycles!) 

It’s normal for periods to last between two and seven days. While it’s normal for the length of your cycle to vary slightly each month, if it varies by more than seven to nine days, then it’s considered irregular. If you notice this happening, it’s a good idea to check in with your health care provider to make sure everything is OK.

Reasons for a late period 

First things first, how late can a period be before pregnancy becomes an option? There’s no one-size-fits-all answer to this question. However, there are some perfectly reasonable alternative explanations for a period that’s gone missing. So, what are they?

During the early stages of puberty, it’s common to have irregular cycles. It’s normal for adolescents to have irregular cycles and a late menstrual cycle for the first few years after they get their period. This is because the ovaries may not be releasing an egg every month yet. However, for people who are past that phase, there are lots of other things that can cause a late period and irregular periods. 

With that in mind, let’s take a look at 12 common causes of a late period.

Average cycle length 

It’s normal for periods to vary a little in length from month to month. But how late can a period be before you should consider reaching out to your health care provider? Generally, a period is considered late if you’re usually regular and it’s more than three days past when it was due. 

Stress

Do you have a late period, but you’re not pregnant? Stress might be the culprit. There are many causes of stress, including:

• Emotional stress caused by work issues, bereavement, money problems, or relationship issues 
• Physical stress caused by surgery, illness, or physical trauma 

Some stress is a regular part of life. However, too much of it can disrupt the body’s hormonal balance, which may result in a late or missed period. 

Stress can interfere with the body’s cycle regulation by affecting the hypothalamus. When we get stressed, our body starts producing more of a hormone called cortisol, which can interrupt the production of hormones required for menstruation to happen. Usually, once the stress level is reduced, menstruation is restored. So, the answer to how long stress can delay your period may depend on whether your stress is short term or chronic.

Proper stress management can be very helpful and includes activities like meditation and exercise. It’s a good idea to speak to your doctor if you think stress is affecting your cycle, as they will be able to run some tests and offer you tailored advice.

Weight loss

Weight fluctuation is another common reason for a late or missed period. Rapid weight loss due to dieting or excessive exercise can also affect the body’s hormones. Staying healthy and maintaining an active lifestyle can help menstrual cycles become regular again, but it’s best to speak to your doctor for tailored advice on this.

Excess weight

Excess weight can affect ovulation by altering the body’s levels of estrogen and progesterone. This can cause irregular periods. Being underweight can also prevent a person from getting their period. 

Extreme exercise 

Have you been hitting the gym hard lately and wondering why your period is late? Extreme physical activity can stop your menstrual cycle because it causes your metabolism to slow down, which in turn can cause ovulation to stop as your body tries to conserve its energy. If you think this is why your period’s gone missing, always speak to your health care provider. 

Birth control

Hormonal birth control can also be responsible for changes to the menstrual cycle. For example, the contraceptive pill causes some people to miss a period every so often. Are you wondering how late a period can be on birth control? Some types of hormonal contraception, such as the progestogen-only pill, contraceptive injection, and intrauterine system, can cause periods to stop completely while you’re using them. It’s also worth noting that the length of time it takes for your period to return after stopping birth control will depend on the type you were using.

Medication

If you’re experiencing a late or missed period, but you know you’re not pregnant, it could be worth checking any medication you’re taking. For example, antidepressants could impact your cycle. If you’re taking any medication and you’re concerned or have any questions, always reach out to your doctor for advice. 

Polycystic ovary syndrome 

PCOS is a common condition that can cause irregular periods. It causes the body to produce a higher amount of androgen, which can prevent an egg from being released (ovulation), leading to delayed or missed periods. In addition to irregular periods, common symptoms of PCOS include: 

• Excess facial hair growth (hirsutism)
• Infertility
• Weight gain
• Acne 
• Thinning hair
• Period symptoms but no period

If any of these symptoms are present in addition to late or irregular periods, a health care provider can perform tests to make a diagnosis and recommend treatment.

Early perimenopause

Perimenopause is the transitional phase before menopause that usually starts in your mid-40s. There are, however, some people who begin perimenopause early, experiencing signs and symptoms as early as their mid-30s. 

Perimenopause is characterized by a decline in estrogen, which then throws your body’s production of progesterone off balance. These two hormones are key for ovulation and menstruation, and so the changes can result in irregular periods. If you’re experiencing perimenopause and still sometimes get your period, it means you’re still ovulating (albeit irregularly). Once you’ve gone 12 months without a single period, it means that menopause has begun.

Primary ovarian insufficiency

Primary ovarian insufficiency (POI) is when a woman’s ovaries stop working normally before the age of 40. This can be another reason behind a late menstrual cycle. 

POI is not the same as early menopause. If your periods stop due to POI, there is a chance they will come back. It’s also possible to have POI and continue to menstruate, ovulate, and even get pregnant. 

If you’re under 40 and have been having irregular periods for four months or longer, your doctor may test for POI. However, know that POI is rare, impacting just 1% of women aged 15 to 44 — so if you’re wondering, “Why is my period late?” it’s likely to be another reason. 

Thyroid disease

A thyroid hormone imbalance may result in a disrupted menstrual cycle. When thyroid hormone levels are too low or too high, it can cause prolonged menstrual bleeding, anovulatory cycles (cycles without ovulation), and irregular periods.

In some cases, thyroid disease can also cause periods to stop for several months, which is called amenorrhea. 

To treat thyroid disease, health care providers may prescribe thyroid hormone replacement for hypothyroidism and thyroid suppression for hyperthyroidism.

Breastfeeding

If you’ve recently had a baby and are fully breastfeeding, it can temporarily stop your periods. This is because the hormone that causes your body to make breast milk can stop the hormones that control your cycle. Crazy, right?

If you combine breastfeeding with bottle-feeding, it might not have the same effect, and your period could arrive as early as five to six weeks after giving birth. 

Pregnancy

Of course, pregnancy is another common cause of late periods. If you’re normally regular and a period is more than seven days late, following sex anytime since the last period started, there’s a chance of pregnancy. Home pregnancy tests can typically determine pregnancy starting on the first day of a late period. These work by detecting human chorionic gonadotropin (hCG), the hormone your body produces when you’re pregnant, in your urine. If a pregnancy test comes up positive, it’s a good idea to book an appointment with your health care provider to chat it through.

When is it time to see a health care provider about a late period?

You might be wondering what to do when periods are late. If any of the following symptoms are present, it’s important to see a health care provider:

• Unexpected heavy bleeding
• Severe pain
• Vomiting and nausea
• Dizziness
• High fever 

But if you have any concerns about a late menstrual cycle, a health care provider can answer questions, offer medical advice, and diagnose and treat any underlying issues. Flo is also a great tool for period tracking, symptom logging, and cycle prediction. You can try to predict when your next period will arrive with our online period calculator.