Quick answer: Periods are irregular if the gap between them is less than 21 days or more than 35 days, according to the NHS. Common causes include puberty, approaching menopause, pregnancy, stress, weight change, PCOS and thyroid problems. Treatment depends on the cause, so see a gynaecologist if your cycle changes or stays irregular.
Almost every woman has an irregular period at some point. A late period during exams, after travel or during illness is common. But periods that are often early, late, very heavy or missing for months need attention. This guide explains what a normal cycle looks like, the common causes of irregular periods, the tests a gynaecologist may suggest, and the treatment options.
Key takeaways
- The average menstrual cycle is around 28 days; under 21 or over 35 days is called irregular.
- Irregular periods are common in the first years after periods start and in the years before menopause.
- PCOS and thyroid problems are two common medical causes that are easy to test for.
- Always take a pregnancy test if a period is late and pregnancy is possible.
- Bleeding between periods, after sex or after menopause should always be checked.
What counts as an irregular period?
A period is irregular if the gap between the start of one period and the next is less than 21 days or more than 35 days. The NHS page on irregular periods notes that the average cycle is around 28 days, and that it is common for it to be a bit shorter or longer. Periods lasting more than 7 days also need a check.
| Feature | Usually normal | Needs a check |
|---|---|---|
| Cycle length | Around 21 to 35 days | Under 21 days or over 35 days |
| Bleeding duration | Up to 7 days | More than 7 days |
| Change in pattern | Occasional late period | Pattern changes or stays irregular |
| Bleeding between periods | None | Any bleeding between periods or after sex |
| After menopause | No bleeding | Any bleeding after menopause |
What causes irregular periods?
Irregular periods can be caused by puberty, approaching menopause, pregnancy, breastfeeding, some types of hormonal contraception, stress, sudden weight loss or gain, and intense exercise. Medical causes include polycystic ovary syndrome (PCOS), thyroid problems, fibroids and, less often, other hormone conditions. The NHS lists PCOS and thyroid problems among the medical causes.
- PCOS: one of the most common causes; see our guide to PCOS vs PCOD
- Thyroid problems: both underactive and overactive thyroid can change your cycle
- Fibroids or polyps: can cause heavy or irregular bleeding
- Lifestyle factors: stress, poor sleep, crash diets and sudden weight change
How common are PCOS and thyroid problems?
Both are common. The WHO fact sheet on PCOS estimates PCOS affects 10 to 13% of women of reproductive age, with up to 70% undiagnosed. A study across eight Indian cities, including Bangalore, found hypothyroidism in 10.95% of adults, and in 15.86% of women compared with 5.02% of men.
These numbers show why your gynaecologist may suggest a thyroid test and hormone tests when your periods are irregular.
What tests are done for irregular periods?
Tests for irregular periods depend on your age and symptoms. Your gynaecologist may suggest a pregnancy test, blood tests for thyroid function, hormones and haemoglobin, and a pelvic ultrasound. Some women may need a Pap smear or, if bleeding is abnormal, an endometrial biopsy to check the lining of the womb.
- Blood tests through our lab investigations
- A thyroid test (TSH, T3, T4)
- A pelvic ultrasound
- An endometrial biopsy in selected cases, especially after 40 or with heavy bleeding
- A hysteroscopy, where a thin camera looks inside the womb, if polyps or other problems are suspected
How are irregular periods treated?
Treatment of irregular periods depends on the cause. If the cause is lifestyle-related, managing stress, sleep and weight often helps. If PCOS or thyroid problems are found, treating them usually improves the cycle. Hormonal treatment may be advised to regulate periods or control heavy bleeding. Fibroids or polyps may need a procedure.
| Cause | Usual approach (doctor-guided) |
|---|---|
| Stress, weight change, exercise | Lifestyle changes and follow-up |
| PCOS | Lifestyle changes, hormonal treatment if needed |
| Thyroid problem | Treatment of the thyroid condition |
| Fibroids or polyps | Medicines or a procedure, depending on size and symptoms |
| Near menopause | Reassurance, and investigation of heavy or unusual bleeding |
Do not start hormone tablets on your own. A gynaecologist will choose the safest option for you.
Do irregular periods affect fertility?
Irregular periods can make it harder to get pregnant because you may not release an egg every month. This does not mean you cannot conceive. Many women with irregular periods get pregnant, sometimes with help. If you are trying to conceive and your periods are irregular, see a gynaecologist early rather than waiting a year.
When should I see a gynaecologist for irregular periods?
See a gynaecologist if your periods are regularly shorter than 21 days or longer than 35 days, last more than 7 days, stop for three months or more, or are very heavy. Also seek advice for bleeding between periods, after sex or after menopause, or if irregular periods come with weight gain, hair growth or acne.
Where is Naina Polyclinic in Yelahanka?
Naina Polyclinic has served families in Yelahanka, Bengaluru, since 1998 from two centres:
- Naina Polyclinic (Kogilu Road): 2, Kogilu Main Rd, Kondappa Garden Layout, Maruthi Nagar, Yelahanka, Bengaluru, Karnataka 560064. Phone: +91 88615 22910
- Naina Polyclinic & Physiotherapy Center (Yelahanka New Town): 2057, 13th B Cross Rd, MIG Sector B, Udaya Layout, Yelahanka New Town, Bengaluru, Karnataka 560064. Phone: +91 96637 44434
Dr. Rama Shankarnarayan sees patients at the Kogilu Road clinic Monday to Saturday, 5:30 PM to 8:30 PM, and at the Yelahanka New Town centre on Monday, Wednesday and Friday, 11:00 AM to 1:00 PM. Sunday is a holiday. Full details are on our contact and appointments page.
Related reading: our guides on PCOS vs PCOD and thyroid test in Yelahanka. You can also learn more about our gynaecology services at Naina Polyclinic.
Frequently asked questions
How many days late is a period considered irregular?
A single late period is common and often due to stress or illness. Your periods are considered irregular if the gap between them is regularly less than 21 days or more than 35 days, as described by the NHS. If a period is late and pregnancy is possible, take a pregnancy test first.
Can stress cause irregular periods?
Yes. Physical or emotional stress can affect the hormones that control your cycle, causing late, missed or irregular periods. Periods usually return to normal once the stress settles. If your periods stay irregular for more than a few months, see a gynaecologist to rule out other causes.
Is it normal to have irregular periods after 40?
Periods often become irregular in the years before menopause, which usually starts in the mid-40s. However, very heavy bleeding, bleeding between periods or bleeding after menopause should always be checked by a gynaecologist, as it may need tests such as an ultrasound or endometrial biopsy.
Which tests are needed for irregular periods?
Common tests include a pregnancy test, thyroid function tests, hormone tests, a blood count for anaemia, and a pelvic ultrasound. Your gynaecologist will choose tests based on your age, symptoms and history. Some hormone tests are timed to particular days of your cycle.
Can irregular periods be treated naturally?
If irregular periods are due to stress, weight change or intense exercise, lifestyle changes such as balanced meals, regular activity and good sleep often help. If a medical cause such as PCOS or a thyroid problem is found, medical treatment may be needed. Always get a proper check before trying remedies.
Book an appointment at Naina Polyclinic
Periods irregular for more than a few months? Call us to see our gynaecologist, or book through our contact page. Kogilu Road: +91 88615 22910. Yelahanka New Town: +91 96637 44434. In an emergency, go to the nearest emergency department.
Medically reviewed by: Dr. Rama Shankarnarayan, MBBS, DGO (Obstetrics and Gynaecology), Naina Polyclinic, Yelahanka. Last reviewed: November 2026.
Disclaimer: This article is for general information only and does not replace advice from a qualified doctor. Please consult a doctor about your own symptoms, tests and treatment.