Understanding the Normal Menstrual Cycle: A Guide for Every Girl

What is a normal menstrual cycle?

Periods are a natural, healthy part of growing up. Your menstrual cycle runs from the first day of one period to the day before the next. Every girl's pattern is a little different, and knowing what is normal helps you feel confident and prepared.

In adults, a cycle usually lasts 21 to 35 days. In the first few years after periods start, 21 to 45 days is normal. A period usually lasts 2 to 7 days.

What counts as normal?

• Your cycle might be exactly 28 days, or a little shorter or longer.
• In the first year or two, your period may come at a different time each month. That is normal while your body settles.
• Your flow may be lighter or heavier than a friend's.
• Mild cramps are common. Some girls get none at all.
• Sore breasts, bloating, tiredness and mood changes before or during a period are common.

Why do cycles vary?

Many things can change the length of your cycle or how your period feels:

• Age: periods are often irregular in the first few years, and again in the years before menopause.
• Hormones: oestrogen and progesterone rise and fall through the month, and their pattern takes time to settle.
• Food and weight: not eating enough, losing a lot of weight quickly, or a large change in weight can change your cycle.
• Stress, illness and travel can delay a period.
• Exercise: very heavy training, especially without enough food, can make periods stop.
• Contraception: hormonal methods such as pills, the injection and the hormonal IUD can make periods lighter, irregular, or stop them for a while. The copper IUD (Copper-T) can make them heavier.
• Health conditions: PCOS and thyroid problems can make periods irregular.
• Pregnancy: a missed period can be a sign of pregnancy.

Keep a simple record

Note the first day of each period, how long it lasts, and how you feel. Use a calendar or a notebook. After a few months, you will know what is normal for you. Our free period and ovulation calculator can estimate when your next period is due. If something changes, you can tell a doctor clearly.

Want to check what you know? Try our menstrual quiz, or read our page on period myths.

When to see a doctor

Most changes in your cycle are nothing to worry about. But talk to a parent or a trusted adult, and see a doctor, if:

• your period lasts more than 7 days;
• you soak through a pad every hour or two, or pass large clots;
• your periods come more often than every 21 days;
• your periods often come more than 45 days apart, or stop for 3 months;
• you bleed between periods or after sex;
• period pain is so bad that you miss school or cannot do your usual things;
• you could be pregnant.

See a doctor if breasts start to develop before 8, or the first period comes before 10, or periods have not started by 15.

Conditions such as PCOS or thyroid problems can cause some of these signs. A doctor can check for them, and it is always better to go early.

Have a question about your period? Call our menstrual helpline on 85888 70999. It answers at any hour.

FAQs

How long is a normal cycle for a girl?

In the first few years after periods start, 21 to 45 days is normal. In adults, cycles usually last 21 to 35 days.

How long is a normal period?

Usually 2 to 7 days. The length can change a little from month to month. A period that lasts more than 7 days needs a doctor's check.

Is it normal for my periods to be irregular?

Yes, in the first year or two. If your periods come more often than every 21 days, more than 45 days apart, or stop for 3 months, see a doctor.

When should I worry about heavy bleeding?

If you soak through a pad every hour or two, pass large clots, or bleed for more than 7 days, see a doctor.

Will my cycle change as I get older?

Yes. It usually becomes more regular in your late teens. It can change again with contraception, after having a baby, and in the years before menopause.

In short

For girls, a cycle of 21 to 45 days is normal in the first few years, and periods usually last 2 to 7 days. Know what is normal for you, keep a simple record, and see a doctor if something on the list above happens.

About Pinkishe Foundation

Pinkishe Foundation is a specialist implementation organisation for menstrual health. We deliver, reliably, in schools and communities across India. Support our work with a donation.

Learn more

• Period and ovulation calculator
• Menstrual myths and facts
• Test your knowledge: take our menstrual quiz