April 19, 2023/Women's Health

8 Reasons Why Your Period Is Late

Stress, extreme diet and exercise, PCOS and, of course, pregnancy could be responsible

woman checking menstrual cycle on calendar

There’s nothing like a late period to add some extra stress to your life. The most obvious culprit — pregnancy — is one possibility, but there are other things that could be going on, too.

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Ob/Gyn Erin Higgins, MD, explains why late periods happen and what to do if yours is nowhere to be seen.

How late can a period be?

Although some people might have periods that arrive with pinpoint predictability, most have a little variation. So, if your period is a day or two late, don’t panic.

“Your menstrual cycle is the length of time from day one of your period to day one of your next period,” Dr. Higgins says. “On average, these cycles are 28 days long, but can range from 21 to 35 days.”

That means that a 28-day cycle one month and a 26-day cycle the next month is probably nothing to worry about. But your period might be considered late if:

  • It’s been more than 35 days since your last period.
  • You’re normally really regular, and your period is more than three days late.

Reasons why your period could be late

A missed period is often the first sign of pregnancy, but there are other reasons for lateness, too. Let’s talk about the various factors that can delay your monthly flow.

1. Pregnancy

When you’re not pregnant, your body sheds the lining of your uterus each month. That’s what’s happening when you have your period.

But when you’re pregnant, the lining of your uterus — where the fertilized egg attaches and grows — thickens and develops more blood vessels. Instead of shedding that lining by having a period, your body continues to build up that lining to support and nourish the developing fetus.

2. Extreme diet and exercise

A healthy diet and regular exercise can do wonders for your health. If you overdo it, though, your body may put a pause on your periods, at least temporarily.

“Athletes who train really hard or anyone who doesn’t get enough calories may stop menstruating,” Dr. Higgins says. “It’s the body’s way of telling you that it doesn’t have enough resources to support a pregnancy.”

When your periods stop due to weight loss, diet or exercise, you’re experiencing secondary amenorrhea. This means you previously had periods, but they’ve stopped. Secondary amenorrhea can happen if you:

  • Eat an extreme, calorie-restricted diet.
  • Have an eating disorder, like anorexia or bulimia.
  • Lose a lot of weight in a short amount of time.
  • Undergo hardcore exercise training, like for a marathon.

3. Polycystic ovary syndrome (PCOS)

PCOS is a hormonal imbalance that interferes with your body’s ability to release an egg (known as ovulation). When you don’t ovulate, you usually don’t have a period.

“Many people with PCOS have irregular, late or missing periods,” Dr. Higgins explains. Other symptoms of PCOS include:

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Healthcare providers diagnose PCOS by checking your symptoms and performing medical tests, when needed. Medication and lifestyle changes can help you manage your symptoms.

4. Stress

Being super stressed out isn’t just a drain on your mental well-being. It can also cause physical symptoms — including delayed or absent periods.

“Minor, everyday stress usually won’t affect your period,” Dr. Higgins notes. “But big-time stressors interfere with your body’s delicate hormone balance, which can ultimately make your period late.”

Some examples of major stress include:

5. Hormonal birth control

Hormonal contraceptives contain progestin or a combination of progestin and estrogen, two hormones that work to prevent pregnancy.

Some hormonal birth control causes a false period, which is known as withdrawal bleeding. This is when you have your hormone-free week with the pill, ring or patch. But if you take your birth control continuously (that is, skipping your hormone-free week), you might have some light spotting or no period at all.

“It’s usually OK to miss a period if you’re taking hormonal contraceptives continuously,” Dr. Higgins states, “but before you try it, ask your healthcare provider to be sure it’s safe for you.”

What if you use another form of birth control, like an intrauterine device (IUD) or a contraceptive implant?

“Amenorrhea is common — and safe — for people who are using the hormonal IUD,” Dr. Higgins says. “It can also occur with Nexplanon® and Depo-Provera®, though it’s less common.”

6. Thyroid conditions

Your thyroid gland is a butterfly-shaped gland at the base of your neck, and it’s one of the many hormonal mechanisms that help dictate your periods. If it’s overactive (hyperthyroidism) or underactive (hypothyroidism), you might have a late period.

“Thyroid problems are common, affecting more than 10% of people who menstruate,” Dr. Higgins says. “They can cause irregular or missing periods but are sometimes mistaken for menopause.”

7. Perimenopause

Perimenopause, or the transition from the reproductive years to menopause, can last a year or two, or it could take several years. During this time, your cycle might be all over the place — 25 days one month and 29 the next.

The average age of menopause is 51, so perimenopause often begins in your 40s or 50s. Usually, perimenopause comes with other symptoms, too, such as:

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“Irregular periods during perimenopause are common,” Dr. Higgins notes, “but if your periods are consistently getting heavier or closer together, see your healthcare provider so they can rule out other causes and help you find relief.”

8. Youth

When you’re young and relatively new to menstruating, it’s rare to immediately settle into a monthly 28-day cycle. Usually, it takes a few years for things to even out. That’s because preteens and teens have an immature hypothalamic-pituitary-ovarian (HPO) axis.

“The HPO axis is the hormonal system that regulates your ovulation and menstrual cycles,” Dr. Higgins explains. “It takes a few years for the HPO axis to mature and regulate your periods.”

Typically, your periods should become more predictable in your late teens and 20s. But if you continue to have irregular periods (or heavy or painful periods), speak with your healthcare provider to get to the bottom of it.

Is it normal to have a late period?

A few days’ difference here and there usually isn’t a big deal, and it happens to almost everyone from time to time. But sometimes, it can signify a medical condition, and if it happens regularly — like you just never have any idea when your period is on its way — then it’s time to involve your healthcare provider.

Dr. Higgins recommends that you keep track of your periods, which will help you realize right away whether something is amiss. Keep a period diary in your calendar, or use an app designed for that purpose. These records can provide valuable information for you and your healthcare provider.

“Your doctor will want to know details about your previous periods so they can determine whether there’s an issue,” Dr. Higgins says. “An occasional late period is often the result of something minor, but if you frequently have late or irregular periods, check with your provider to rule out other health conditions.”

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