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 period a few days off is usually ordinary variation. There is no official number of days that makes a period “late” — the NHS doesn’t set one. This site uses 7 or more days past the expected date as a working line, taken from FIGO’s regularity band (cycles vary by up to 7–9 days); the late period calculator counts your days. If you could be pregnant, take a test. If you’ve missed 3 periods in a row, see a GP (NHS).
Feeling PMS-type cramps while the period itself is late usually means ovulation shifted this cycle — the symptoms arrived, the bleed hasn’t yet.
What to do first
The first step depends on one question: could you be pregnant?
- The expected date has passed
Demo: expected Oct 1 (last period Sep 3, 28-day cycle).
- Pregnancy possible, or not sureTake a home test
Reliable from the first day of the missed period (NHS). Negative but you still think you could be pregnant? Wait a few days and test again (Demo: Oct 8 → Oct 11). Second test negative and still no period: speak to a GP (NHS).
Pregnancy not possibleWait — and note what changedStress, illness, travel, training, weight, new medicine or contraception, breastfeeding. One late period after a change like that usually sorts itself out.
The 10 common causes
| Cause | How it delays your period | Typical clue |
|---|---|---|
| 1. Pregnancy | The most famous cause. | If you have had unprotected sex, a home pregnancy test is reliable from the first day of the missed period (NHS). If it’s negative and you still think you could be pregnant, wait a few days and test again; speak to a GP if the second test is negative and your period still hasn’t come (NHS). |
| 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; the NHS lists doing too much exercise as a common cause. | 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. | Emergency contraception is a special case — the morning-after pill can shift your next period by up to about a week (Mayo Clinic); if 3 weeks pass with no period after taking it, take a pregnancy test. |
| 7. Postpartum and breastfeeding | Lactation hormones suppress ovulation, which is why periods often stay away during breastfeeding. It can only work as contraception under strict conditions — baby under 6 months, breast milk only with frequent feeds, no period or spotting yet — and it isn’t a guarantee (NHS). | For the full postpartum picture — timing by feeding method, lochia vs period, and red flags — see our guide to the first period after birth. |
| 8. Perimenopause | Usually between the ages of 45 and 55 (NHS), cycles 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 / PMOS | Polycystic ovary syndrome — which the NHS now calls polyendocrine metabolic ovarian syndrome (PMOS) — 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
One late period is usually your body being human. These are the points where it’s worth being seen:
- Don’t waitSevere pain, very heavy bleeding, fever, or new headaches or vision changes with missed periods
Get seen promptly.
- 3 in a rowYou’ve missed your period 3 times in a row
See a GP (NHS). You don’t have to wait that long if something else on this list applies.
- With other changesA missed period plus weight gain or loss, tiredness, facial hair, or dry or oily skin
See a GP (NHS); a blood test can check hormones such as thyroid.
- A new patternYour periods have become irregular
See a GP (NHS). Bring your recorded start dates.
- TeensNo periods by age 15
See a GP (NHS).
Frequently asked questions
How late is too late to worry?
There is no official number of days — the NHS doesn’t set one. A few days is ordinary variation; this site uses 7 or more days past the expected date as a working line for “late”. What matters more is what’s happening: if you could be pregnant, test (and see a GP if a repeat test is negative and the period still hasn’t come); and see a GP if you’ve missed 3 periods in a row, a missed period comes with other symptoms such as weight change or facial hair, or your periods have become irregular (NHS). You don’t need to wait months to ask.
Can I be late and not pregnant?
Absolutely — stress, weight change, exercise, illness, contraception changes, PCOS and thyroid issues are all common non-pregnancy causes.
Will my period come if I take a negative test?
Usually yes — a negative with a late period most often means one of the non-pregnancy causes on this page, or that ovulation simply ran late. But a negative is less reliable than a positive, especially if you tested early. If you still think you could be pregnant, wait a few days and test again; if the second test is negative and your period still hasn’t come, speak to a GP (NHS).
Can emergency contraception (Plan B) make my period late?
Yes. The morning-after pill works partly by delaying ovulation, so the period that follows can arrive earlier or later — Mayo Clinic notes a delay of up to about a week. If your period has not come within 3 weeks of taking it, take a pregnancy test.
My pregnancy test is negative but my period still hasn't come — what now?
Most home tests are reliable from the first day of a missed period, but a negative is less reliable than a positive — testing too early or not following the instructions can give a false negative (NHS). Wait a few days and test again. If the second test is also negative and your period still hasn’t come, speak to a GP (NHS) — you don’t need to wait for months. If you don’t know when your period was due, test at least 21 days after you last had unprotected sex (NHS).
Why is my period late but I have cramps?
Cramps without bleeding usually mean ovulation happened later than usual this cycle — PMS-type symptoms can arrive on schedule while the bleed itself is still days away. A shift of a few days is normal variation: cycles count as regular when the year's shortest and longest differ by less than about 7–9 days (FIGO).
My cycle is always regular — is 1–3 days late something to worry about?
No. Even clockwork cycles have normal variation: a normal adult cycle is 24–38 days, and up to 7–9 days of difference between your shortest and longest cycle in a year still counts as regular (FIGO). There is no official day count for “late”; this site’s working line is 7 or more days past your expected date. If you could be pregnant, a test is reliable from the first day of the missed period (NHS).
References
- American College of Obstetricians and Gynecologists — Amenorrhea: Absence of Periods
- Mayo Clinic — Menstrual cycle: What's normal, what's not
- Mayo Clinic — Morning-after pill
- Cleveland Clinic — Abnormal Menstruation (Periods)
- NICHD — What causes menstrual irregularities?
- NHS — Missed or late periods (reviewed 12 June 2026)
- NHS — Doing a pregnancy test (negative results; page reviewed 9 February 2022)
- NHS — Natural family planning (lactational amenorrhoea method)