First: what does "late" actually mean?
A period is generally considered late if it hasn't arrived more than 7 days past its expected date. Normal cycle variation of 1–3 days from month to month is completely common. If you are sexually active and your period is 7+ days late, take a pregnancy test first before investigating other causes.
10 common reasons for a late period
1. Stress
Stress is the most common non-pregnancy cause of a late period. Elevated cortisol interferes with the hormonal cascade (GnRH → FSH → LH) that triggers ovulation. Since your period arrives approximately 14 days after ovulation, delayed ovulation directly delays your period. This can happen with acute stress (exam week, bereavement) or chronic stress.
2. PCOS (polycystic ovary syndrome)
PCOS affects approximately 10% of the population and causes irregular or absent ovulation due to elevated androgens. Cycles can vary widely — from 35 days to several months. If you have infrequent periods alongside acne, excess body hair, or weight management difficulties, PCOS is worth discussing with a doctor.
3. Thyroid disorders
Both hypothyroidism (underactive thyroid) and hyperthyroidism (overactive) can disrupt cycle regularity. Hypothyroidism is particularly associated with longer, heavier cycles. A simple TSH blood test can rule this out.
4. Significant weight loss or gain
Body fat is involved in estrogen production and regulation. Very low body weight or body fat can shut down the reproductive axis (hypothalamic amenorrhoea), causing periods to stop or become very infrequent. Rapid weight gain can also disrupt hormone balance, particularly in PCOS.
5. Intense or sudden change in exercise
High-volume, high-intensity exercise — particularly when combined with low energy availability — can suppress ovulation through the same hypothalamic pathway as stress. This is called the Female Athlete Triad and is common in competitive athletes, distance runners, and ballet dancers.
6. Illness or fever
A significant illness, especially with a high fever, can delay ovulation in the cycle during which you were ill. The period will typically arrive late but return to its normal schedule afterward.
7. Stopping hormonal contraception
After stopping the combined pill, mini-pill, hormonal IUD, implant, or contraceptive injection, it can take several weeks to several months for cycles to resume their natural rhythm. This is called post-pill amenorrhoea and is temporary in most cases, though the injection (Depo-Provera) can delay the return of periods for up to 12–18 months.
8. Perimenopause
The hormonal transition before menopause typically begins in the mid-to-late 40s but can start earlier. Cycles become increasingly irregular — varying in length and eventually stopping. If you're over 40 and experiencing irregular periods, this is a likely cause.
9. Travel and time zone changes
Significant travel across time zones can disrupt circadian rhythms enough to delay ovulation, especially in the cycle during which you travel. The effect is usually temporary.
10. Breastfeeding
Prolactin — the hormone that drives milk production — suppresses ovulation. Most breastfeeding people experience delayed return of periods (lactational amenorrhoea). The effect depends on frequency and exclusivity of breastfeeding.
When to see a doctor
- Pregnancy test positive — confirm with a doctor
- Period is more than 2–3 weeks late with negative test
- 3 or more periods missed (secondary amenorrhoea) without a known cause
- Cycles have been irregular for 3+ consecutive months