Why Is My Period Late? 11 Common Reasons

A late period is one of the most stressful cycle experiences — even when you're not trying to conceive. If your period hasn't arrived when you expected it, you're not alone.

Cycles vary, and there are many reasons your period might be running late that have nothing to do with pregnancy. This article covers the most common causes of a late period and what you can do to understand your cycle better. It is for informational purposes only and does not constitute medical advice. If you have concerns about your cycle, speak with a healthcare provider.

First — what counts as “late”?

A typical cycle is between 21 and 35 days. If yours usually runs 28 days and it's now day 32, it feels late — but it may still be within a normal range. Cycles naturally vary by a few days from month to month. A period is generally considered late if it hasn't arrived more than 5 days after your expected date based on your recent cycle history.

Tracking your cycle over several months gives you a personal baseline — which is more useful than comparing to an “average” cycle.

11 common reasons your period might be late

1. Stress

High physical or emotional stress can affect the hormonal signals that regulate your cycle. The hypothalamus — which controls hormone release — is sensitive to stress. A particularly difficult month, a big life event, or prolonged anxiety may delay ovulation and push back your period.

2. Illness or recent infection

Being unwell can temporarily disrupt your cycle. Your body prioritises recovery, which may delay ovulation. Even a short illness like a cold or flu can shift your cycle by several days.

3. Changes in weight or diet

Significant weight loss, weight gain, or a major change in eating habits can affect hormone levels and delay your period. This includes very low calorie intake or starting a new restrictive diet.

4. Intense exercise

High-intensity training or a sudden increase in exercise can affect oestrogen and progesterone levels. Athletes or people who have recently started heavy training may notice cycle disruption.

5. Travel or schedule changes

Crossing time zones or a major shift in your sleep schedule can temporarily affect your hormonal rhythms. This is more common after long-haul travel.

6. Coming off hormonal contraception

If you've recently stopped the pill, hormonal coil, implant, or injection, your cycle may take several months to regulate. This is normal — your body is re-establishing its own hormonal rhythm. See our guide on tracking your cycle after birth control.

7. Thyroid issues

An underactive or overactive thyroid can affect your menstrual cycle, including causing late, irregular, or missed periods. Thyroid conditions are common and often undiagnosed. Learn more about hypothyroidism and cycle changes.

8. PCOS

Polycystic ovary syndrome is one of the most common causes of irregular or late periods. It affects ovulation, which directly affects when — or whether — your period arrives each cycle. Read more about irregular periods and PCOS.

9. Perimenopause

If you are in your late 30s or 40s, hormonal changes associated with perimenopause can cause cycles to become irregular, longer, or less predictable.

10. Significant life changes

Starting a new job, moving house, grief, or any major disruption to your routine can affect your cycle. The mind-body connection in hormonal health is real, even if it's often overlooked.

11. It's just natural variation

Sometimes there is no identifiable reason. Cycles vary. A one-off late period with no other symptoms is often just natural variation and not a cause for concern.

When should you take a pregnancy test?

If there is any chance of pregnancy, take a test. Home pregnancy tests are most accurate from the first day of your missed period onwards. A negative result followed by a continued absence of your period is worth discussing with your doctor.

When should you see a doctor?

Speak with a healthcare provider if:

• Your period is more than 3 months late
• You have sudden changes to a previously regular cycle
• You are experiencing other symptoms such as unusual hair loss, weight changes, or fatigue alongside a late period
• You are trying to conceive

How tracking can help

Tracking your cycle over time — including sleep, energy, stress, and symptoms — gives you real data to share with a doctor and helps you spot patterns you might otherwise miss.

This article is for informational purposes only. It does not replace professional medical advice, diagnosis, or treatment. If you have concerns about your menstrual cycle or are experiencing symptoms that worry you, speak with a qualified healthcare provider.