Why is my period late? 10 common causes

A late period is one of the most searched health questions on the internet, and most of the time the cause is temporary. Here are the ten usual suspects, and the line between "wait and see" and "see a doctor".

First, what counts as late

A cycle that arrives a few days off its predicted date is normal variation, not a late period. Guidance from professional bodies generally treats a period as late about a week or more past the expected date, and as missed around 90 days. Use a late period calculator to see exactly where you stand.

1. Pregnancy

The most famous cause. If you have had unprotected sex and your period is about a week late, a home pregnancy test is usually reliable. Test with first-morning urine; if negative and your period still does not arrive, retest a week later.

2. Stress

Physical and emotional stress can delay or suppress ovulation by interfering with the hypothalamus, the brain region that runs the cycle. No ovulation, no period on schedule — it simply arrives late, once the stress settles.

3. Weight change

Significant loss or gain, and very low body fat, can disrupt the hormones that trigger ovulation. Both under-eating and rapid weight gain are well-recognized causes of late or missed periods.

4. Intense exercise

High training loads combined with low energy availability can suppress ovulation — common in endurance athletes. It typically reverses when training or nutrition changes.

5. Illness or travel

A bad viral illness, a shift-work schedule or a long-haul trip can nudge the cycle's timing for one month. These one-off delays are exactly the kind that resolve on their own.

6. Birth control changes

Starting, stopping or missing hormonal contraception reshapes cycles. After stopping, periods can take weeks to months to find their old rhythm; some methods (hormonal IUDs, implants, continuous pills) make periods light or absent by design.

7. Postpartum and breastfeeding

Lactation hormones suppress ovulation, which is why periods often stay away during breastfeeding — though not reliably enough to count on as contraception.

8. Perimenopause

From the mid-40s on average, cycles naturally become shorter, longer or skipped as hormone levels shift. Late periods in this window are expected, though heavy bleeding still deserves a check.

9. PCOS

Polycystic ovary syndrome is the most common cause of persistently irregular or absent periods, often with acne, excess hair growth or weight changes. It is very treatable — but only if evaluated.

10. Thyroid and other hormonal conditions

An over- or under-active thyroid, high prolactin and other endocrine issues can delay or stop periods. A simple blood test screens for them.

When to see a doctor

Three or more months without a period (pregnancy ruled out), cycles suddenly much more irregular, severe pain, very heavy bleeding, fever, or new headaches and vision changes alongside missed periods — all warrant prompt evaluation. One late period, by contrast, is usually your body being human.