Quick answer: Irregular periods are cycles shorter than 21 days, longer than 35 days, or varying by more than about a week from month to month. Common causes are PCOS, thyroid disorders, high prolactin, stress, weight change and perimenopause. Treatment targets the cause and may include lifestyle changes, hormonal medicines or ovulation induction.
Key takeaways
- Always rule out pregnancy first when a period is late or unusual.
- PCOS is the most common cause of irregular periods in women of reproductive age.
- Simple blood tests (TSH, prolactin, hormones) and an ultrasound find the cause in most cases.
- Treatment depends on the cause and on whether you want to get pregnant.
- Untreated long gaps between periods can thicken the uterine lining, so regular review matters.
What counts as an irregular period?
A period is irregular when the gap between periods falls outside 21 to 35 days, or changes unpredictably from cycle to cycle. Occasional variation of a few days is normal.
- Infrequent periods: cycles longer than 35 days, or fewer than eight or nine periods a year.
- Frequent periods: cycles shorter than 21 days.
- Unpredictable cycles: the shortest and longest cycles differ by more than about 7 to 9 days.
- Missed periods: no period for three months or more (secondary amenorrhoea).
For a wider look at every type of cycle change, see our complete guide to period issues.
What causes irregular periods?
Irregular periods usually mean ovulation is not happening on a regular schedule. The causes below are the ones a gynaecologist checks first.
| Cause | Typical clues | Key test |
|---|---|---|
| Pregnancy | Late period, nausea, breast tenderness | Urine or blood hCG |
| PCOS | Long cycles, acne, excess hair, weight gain | Ultrasound, testosterone, LH/FSH |
| Thyroid disorder | Tiredness, weight change, feeling hot or cold | TSH, free T4 |
| High prolactin | Missed periods, milky nipple discharge, headaches | Prolactin |
| Stress, under-eating, over-exercise | Recent weight loss, heavy training, high stress | Low LH/FSH and oestrogen |
| Perimenopause | Age 40s, hot flushes, cycle changes | Clinical; FSH sometimes |
| Premature ovarian insufficiency | Under 40, missed periods, hot flushes | Repeated high FSH, low AMH |
Other causes include hormonal contraception (especially in the first months or after stopping), breastfeeding, some medicines, diabetes, and structural problems such as polyps or fibroids, which more often cause bleeding between periods. If your cycle changed suddenly as an adult, read sudden irregular periods in your 20s and 30s. For teenagers, see irregular periods in teenagers.
How are irregular periods diagnosed?
Diagnosis begins with your history and usually needs only a few tests. Bring a record of your last three to six cycles if you can.
- History: cycle pattern, weight change, stress, exercise, medicines, acne or hair growth, and pregnancy plans.
- Examination: weight, blood pressure, signs of excess androgens, and a pelvic examination when appropriate.
- Blood tests: pregnancy test, TSH, prolactin, and LH, FSH, oestradiol, testosterone or AMH as needed. Fasting glucose and lipids are useful in PCOS.
- Pelvic ultrasound: to look at the ovaries and the thickness of the lining.
- Endometrial sampling: considered when periods have been infrequent for a long time, especially over 45 or with risk factors such as obesity.
What are the treatment options for irregular periods?
Treatment depends on the cause and on what matters most to you: a regular cycle, symptom control or a pregnancy.
Lifestyle changes
In PCOS, losing even 5 to 10 percent of body weight can restore ovulation in many women. In stress-related or low-weight cycles, eating enough, easing exercise and improving sleep are the main treatment.
- Eat regular, balanced meals with enough protein and complex carbohydrates; avoid crash diets.
- Aim for about 150 minutes of moderate exercise a week, without sudden jumps in intensity.
- Keep a steady sleep routine, and limit night shifts where possible.
- Track your cycle in an app or diary so your doctor can see the pattern.
Treating the underlying condition
Thyroid tablets correct hypothyroidism, and medicines such as cabergoline lower high prolactin. Periods often become regular once these are controlled.
Hormonal treatment
Combined oral contraceptive pills, cyclical progestogens or a hormonal IUD regulate bleeding and protect the uterine lining in women who are not trying to conceive.
Fertility treatment
If you want a pregnancy, ovulation induction with letrozole or clomiphene helps the ovaries release an egg. Our article on letrozole vs clomid for PCOS compares the two. Metformin may help some women with PCOS and insulin resistance.
Can irregular periods affect fertility and long-term health?
Yes. Irregular cycles often mean irregular ovulation, which makes it harder to time conception. Long gaps without a period also expose the lining to oestrogen without progesterone, which over years raises the risk of endometrial hyperplasia. PCOS is linked with diabetes, high cholesterol and sleep apnoea, so long-term check-ups matter. Low-oestrogen causes such as hypothalamic amenorrhoea can thin the bones.
When to see a gynaecologist
- No period for three months and a negative pregnancy test.
- Cycles consistently shorter than 21 or longer than 35 days.
- Very heavy or prolonged bleeding, or bleeding between periods.
- Acne, excess hair growth or rapid weight gain with irregular periods.
- Milky nipple discharge, headaches or vision changes.
- Trying to conceive for 12 months (6 months if over 35) without success.
How Dr. Divya Venugopalan can help
Dr. Divya Venugopalan is a gynaecologist and fertility specialist in Bengaluru and a member of the PCOS Society. She finds the cause of irregular periods with focused tests and builds a plan around your goals, whether that is a predictable cycle or a pregnancy.
For women trying to conceive, her fellowship in reproductive medicine (FRM) guides ovulation induction and, when needed, IUI. Her gynaecology care also covers thyroid and hormone-related cycle problems.
She consults at Thanisandra, Sahakar Nagar and HRBR Layout. Book an appointment or call +91 99459 26987.
Frequently asked questions
How long can a period be late before I should worry?
If a pregnancy test is negative, one late period is usually not a concern. See a doctor if you miss three periods in a row or if your cycles are consistently longer than 35 days.
Can irregular periods be cured?
Many causes, such as thyroid problems or high prolactin, can be corrected. PCOS cannot be cured, but it can be well controlled with lifestyle changes and medicines so that cycles become regular.
Can I get pregnant with irregular periods?
Yes. Many women with irregular periods conceive, sometimes with help. Ovulation induction with tablets such as letrozole is often effective, especially in PCOS.
Do birth control pills fix irregular periods?
The pill creates regular withdrawal bleeds and protects the uterine lining, but it does not treat the underlying cause. Your periods may become irregular again after stopping it.
Can stress alone cause irregular periods?
Yes. Significant stress, poor sleep or under-eating can suppress the brain signals that control ovulation. A doctor should still rule out other causes before putting it down to stress.
Medically reviewed by: Dr. Divya Venugopalan, MBBS, DNB (OBG), FRM, FMAS. Gynaecologist & fertility specialist, Bengaluru (KMC Reg. No. 91293). Last reviewed: 27 October 2026.
This article is for general information and does not replace a personal consultation. In an emergency, visit the nearest hospital emergency department.
