The short answer: Your periods are irregular if the gap between them is often shorter than 21 days or longer than 35 days, or if it changes a lot from one month to the next. Common reasons include puberty, approaching menopause, stress, big weight changes, too much exercise, PCOS, thyroid problems, hormonal contraception, pregnancy and breastfeeding. Irregular periods aren't always a sign of a problem, but it's worth seeing a doctor, especially if they come with other changes in your body.
What counts as an irregular period?
To know whether your periods are irregular, you first need to know your cycle length. Count from the first day of bleeding in one period (day 1) to the day before your next period starts. The average cycle is around 28 days, but anywhere between 21 and 35 days is considered normal.
- Regular: your cycle falls between 21 and 35 days, and it only shifts by a few days each month. A cycle of 30 days, then 27, then 31 is regular.
- Irregular: your cycle is often shorter than 21 days or longer than 35, you skip periods, or the gap is very different each time. A cycle of 24 days, then 45, then 30 is irregular.
Periods that last more than 7 days, or bleeding between periods, are also worth checking, even if your cycle length is in the normal range. If you'd like help counting, our guide on how to calculate your next period date has worked examples.
Why tracking matters
Most women don't remember their dates accurately. Mark the first day of every period on your phone calendar, in a period app or in a small diary. After three or four months, you'll see your real pattern, and your doctor will be able to help far more quickly.
Common causes of irregular periods
Your cycle is controlled by a chain of hormones from the brain to the ovaries. Anything that disturbs that chain, from a stressful month to a thyroid problem, can change when ovulation happens, and so when your period comes.
| Cause | What to look out for |
|---|---|
| Puberty | Cycles are often irregular in the first few years after periods start |
| Approaching menopause | From the mid-40s, cycles often become shorter, longer or unpredictable |
| Stress and anxiety | Exams, work pressure, family worries or big life changes can delay ovulation |
| Weight loss or gain | Sudden or large changes in either direction can upset your hormones |
| Too much exercise | Especially intense training without eating enough to fuel it |
| PCOS | Long gaps between periods, often with acne, extra hair growth or weight gain |
| Thyroid problems | Tiredness, feeling too hot or too cold, weight changes, hair thinning |
| Hormonal contraception | The progestogen-only pill, injection and hormonal IUD can make bleeding irregular |
| Pregnancy | A missed period is often the first sign |
| Breastfeeding | Can delay the return of periods for months after birth |
| Other health conditions | Diabetes, heart disease and some medicines can affect your cycle |
Puberty and the teenage years
It can take a few years after the first period for the cycle to settle into a pattern, because ovulation doesn't always happen every month at first. Gaps of six or eight weeks are common in the first year or two. See a doctor if periods are very heavy, very painful, or stop for several months.
Perimenopause
Menopause usually happens between 45 and 55. In the years before it, called perimenopause, ovulation becomes less predictable. Periods may come closer together, further apart, heavier or lighter. Our guide to perimenopause covers this stage in detail.
Stress, weight and exercise
Your brain treats severe stress, sudden weight loss or very intense exercise as signals that it's not a good time for pregnancy. It can switch down the hormones that trigger ovulation. Students preparing for board exams, women dealing with a family illness, and athletes who train hard while eating too little are all at risk of delayed or missed periods.
PCOS
Polycystic ovary syndrome is one of the most common hormone conditions in women and a frequent cause of long gaps between periods. Experts have recently renamed it polyendocrine metabolic ovarian syndrome (PMOS), and the NHS now uses the new name. Many doctors in India still say PCOS or PCOD. Read our full guide to PCOS if this sounds familiar.
Thyroid problems
Both an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism) can affect your periods. Both are easy to check with a simple blood test.
Irregular, late or missed?
These terms overlap, but they're not quite the same. An irregular period means your pattern keeps changing. A late or missed period is a single period that hasn't arrived when expected. If your period is late and you've had sex, the first step is always a home pregnancy test. Our guide on reasons your period is late but you're not pregnant explores the other possibilities.
Going three months or more without a period, when you're not pregnant, breastfeeding or past menopause, is always worth seeing a doctor about.
What a doctor will ask and check
You can see your family doctor, a gynaecologist, or a doctor at your local government health centre. Take your period dates with you. Your doctor will probably ask:
- When your periods started and what your cycle has been like
- How long you bleed and how heavy the flow is
- Whether you've noticed weight changes, acne, extra facial or body hair, hair thinning, tiredness or mood changes
- About stress, diet, exercise and sleep
- What contraception or other medicines you use
- Whether you're trying to get pregnant
Tests you might be offered
- A pregnancy test: to rule out pregnancy first.
- Blood tests: to check thyroid hormones, reproductive hormones, prolactin (a hormone that can stop periods when raised), blood sugar and sometimes haemoglobin.
- A pelvic ultrasound: to look at your womb and ovaries. For adults, this may be done through the tummy or as an internal scan. For teenagers, scans are used less often, as ovaries can naturally look busy at this age.
These tests are widely available at diagnostic labs and government hospitals in India. Ask your doctor which ones you actually need, rather than booking a large package.
How irregular periods are treated
Treatment depends on the cause, and sometimes no treatment is needed at all. If your periods are irregular because you're 14 or 47, your doctor may simply reassure you and ask you to keep tracking.
- PCOS: your doctor may suggest certain contraceptive pills to make periods more regular, alongside lifestyle changes. Other medicines can help if you're trying to get pregnant.
- Thyroid problems: treating the thyroid with medicine usually settles the cycle.
- Weight or exercise-related: reaching a healthy weight, and eating enough to fuel your training, often brings periods back.
- Raised prolactin: medicine can lower it, and periods often return.
- Contraception side effects: your doctor may suggest giving it more time or trying a different method.
What you can do yourself
- Track every cycle: start date, number of bleeding days, how heavy the flow is and any symptoms.
- Eat regular, balanced meals: skipping meals and crash diets can both upset your hormones. Build meals around dal, vegetables, whole grains such as ragi, jowar or brown rice, and some protein like eggs, paneer, curd or chana.
- Keep active, without overdoing it: 30 minutes of walking, yoga or cycling on most days is plenty for most people.
- Protect your sleep: keep regular hours if you can. If you work night shifts, try to keep your sleep times consistent across the week.
- Manage stress in ways that suit you: exercise, prayer, breathing exercises, time with friends, or talking to a counsellor.
- Look after your iron levels: if you sometimes get heavy periods after a long gap, include iron-rich foods such as palak, rajma, jaggery and dates, with amla or lemon to help absorption.
Being ready when you can't predict your period
The hardest part of irregular periods is not knowing when the next one will arrive. A period that comes after a long gap can also be heavier than usual. A few habits help:
- Wear a panty liner on days you think your period might start, especially if you usually get some spotting first.
- Switch to a period panty when you notice early signs like cramps, bloating or sore breasts. Its built-in absorbent layers mean an unexpected start doesn't catch you out at college or work.
- Keep a small pouch in your bag with a spare panty or pad and a few wipes, so you're ready wherever you are.
Irregular periods and getting pregnant
Irregular periods can make it harder to get pregnant, because you may not be ovulating every month, and it's harder to know when your fertile days are. If you're trying for a baby, having sex every two or three days through your cycle, without contraception, can help.
If you've been trying for a while without success, speak to a doctor. There are tests to check whether you're ovulating, and treatments, including medicines that help you ovulate, if you're not.
See a doctor if
- Your periods are irregular, or your usual pattern has changed
- You've missed three periods in a row and you're not pregnant
- Your periods last longer than 7 days
- You bleed between periods
- Irregular periods come with weight gain, tiredness, facial hair growth, or very dry or oily skin
- Your periods haven't started by age 15
- You're struggling to get pregnant
Get urgent help if
Call 112 or 108, or go to the nearest hospital emergency department, if you have very heavy bleeding (soaking through a pad or period panty every hour for a few hours), feel faint or dizzy, or could be pregnant and have severe tummy pain on one side.
Frequently asked questions
Is it normal for teenagers to have irregular periods? Yes. It can take a few years after periods start for the cycle to settle. See a doctor if periods are very heavy, very painful, or stop for several months.
Can irregular periods go back to normal on their own? Often, yes, especially if the cause was stress, illness or a short-term change. If they stay irregular for several months, get checked.
Do irregular periods mean I have PCOS? Not necessarily. PCOS is one common cause, but there are many others. A doctor can work out which applies to you.
Can stress really delay my period? Yes. Severe stress can delay ovulation, which pushes your period later. It usually settles once the stressful time passes.
Is a 40-day cycle normal? Once in a while, it can happen. If your cycles are often longer than 35 days, see a doctor to check for causes such as PCOS or a thyroid problem.
Are home remedies enough to regulate periods? Healthy eating, exercise, sleep and stress relief help many women. But if there's an underlying cause such as a thyroid problem, it needs proper treatment, so get checked first.
Related reading
- PCOS vs PCOD: What's the Difference?
- Period Came Early? 9 Reasons and When to Worry
- Heavy Periods: How Much Bleeding Is Too Much?
- Why Is My Period Lasting Longer Than Usual?
This article is for general information and doesn't replace advice from your doctor.
Sources: NHS: Irregular periods, NHS: Missed or late periods, NHS: Polyendocrine metabolic ovarian syndrome (PMOS)