Help! Why Is My Period Late? 5 Possible Reasons

The most common cause of a missed period is pregnancy! A home pregnancy test is easy and accurate. If your period is late, but you’re not pregnant, do investigate, but don’t worry: most menstruating people will experience this situation at least once in their lifetime. Irregular cycles are quite common and affect around 25% of women in the United States.¹ But what counts as an irregular or “normal” cycle is actually unique to each person.

What is a late period?

While medical sources vary in their exact definition of a late period, your time frame will depend on the type of cycle you regularly experience.

If you have a regular cycle, your period is considered late if it’s overdue by three to five days.²³ 

What is an irregular period?

Though we typically think of regular menstruation as a 28-day cycle — counted from the first day of period bleeding until the day before the next period begins — it does vary for each person. A normal cycle with regular periods should at least have the following components:⁴

• The cycle lasts between 21 and 35 days 
• The bleeding lasts two to seven days
• The heaviest bleeding occurs within the first three days 

Irregular cycles will include constantly changing cycle lengths, brief or extended periods, irregular menstrual bleeding and bleeding between periods.

Things that delay your period

Some irregularity is normal during the first few years of menstruation or menopause,⁵ but if you’re well into your reproductive years, there may be other things to blame. Aside from pregnancy, late or missed periods can be a result of changes to reproductive hormones or various medical conditions. Here are six common causes for late periods:

1. You're more stressed than usual

When your stress levels are high, your body releases the stress hormone cortisol. Cortisol can affect the hypothalamus and hormones needed for menstruation. It is believed that this is the mechanism where high or chronic stress can affect and cause period delays. 

2. Perimenopause

In the United States, the average age of menopause is 52, and the transition time leading up to it — usually lasting about four years though it can vary and be longer — is called perimenopause.⁶ This transition period may include hot flashes, trouble sleeping and irregular periods.  

3. Extreme diet and exercise 

Major lifestyle changes, like drastically reducing your calorie intake or engaging in excessive exercise, can put stress on the body and cause late or missed periods.⁷  

It is estimated that female body fat percentage should be approximately 22% for menstruation to occur.⁸ Insufficient fat stores make it hard for the hypothalamic axis — the interactions of the hypothalamus, pituitary and adrenal glands which drive menstruation — to get the energy it needs to do its job. That’s why calorie-restrictive eating disorders, excessive exercise disorders and intense athletic scenarios where lean body mass is essential (gymnastics, distance running, etc.) can affect the menstrual cycle. In these cases, low body fat leads to low estrogen, which leads to interrupted menstruation. This scenario can also be bad for your bone health, so be sure to talk to your doctor if this sounds like you.

4. Birth control and medications

Hormonal birth control can affect your menstrual cycle — often, that’s the point! Beyond its contraceptive uses, hormonal birth control can be used to regulate cycles, decrease dangerously heavy flow, decrease the number of cycles you have and help treat the causes of painful cycles. Obstetrician-gynecologists are specially trained to know which method may be useful to treat a particular problem. 

Other medications like steroids or antipsychotics may also affect your flow as a side effect.⁹

5. An existing chronic condition

Any chronic condition has the potential to affect the menstrual cycle. Some good examples include uncontrolled diabetes, thyroid disease or reproductive causes like polycystic ovary syndrome.¹⁰¹¹ Maintaining healthy habits, such as eating a healthful diet and exercising regularly, can help prevent chronic conditions from flaring and affecting your menstrual cycle. 

What should you do when your period is late?

First, take a pregnancy test. If you’re not pregnant and this is your first late period, there’s probably not much cause for concern. Still, you can always take a few steps towards a healthy cycle:

• Track your flow: Keep track of your periods to establish what your regular cycle looks like. Include the time between periods, length of bleeding, daily amount of blood and other symptoms like cramps. This information will be helpful if you need to consult a doctor. 
• Make lifestyle changes: If you’re stressed, undereating or over-exercising, you may want to make some changes to your daily routine or see an expert for help.

When should you see your doctor?

There are several cases when consulting a doctor is advised so they can perform blood tests and assess you for various health conditions:¹²¹³

• No period for months (over 90 days)
• Typically regular periods suddenly become irregular
• Menstrual cycles last less than 21 days or more than 35 days
• Bleeding lasts more than seven days
• Heavy bleeding (i.e., soak through pads and tampons every hour or two) or passing large clots during periods
• Breakthrough bleeding between periods
• Periods become extremely painful or cause nausea and vomiting
• Experience symptoms of toxic shock syndrome (fever, vomiting, diarrhea, fainting and dizziness) after using tampons

Summary

Minor fluctuations in your menstrual cycle aren’t a big cause for concern, especially if you’re just starting to get periods or have begun transitioning into menopause. But if your cycle falls outside the standards of “normal” — your period is extremely heavy, irregular or lasts much longer than a week — it may be time to seek medical attention and rule out a condition that could be affecting your reproductive health.