What Is a Normal Menstrual Cycle?

Your friend’s period comes every 28 days, on schedule, like a train. Yours shows up on day 25, then day 33, then day 27. Last month it lasted four days, this month it’s seven. You aren’t sure if you’re the exception, or if everyone stopped talking about it after middle school.

How long a period lasts and how much you bleed

The NHS² says periods typically last 2 to 7 days, usually around 5, with most of the bleeding in the first two days. It says you lose about 20 to 90ml, or 1 to 5 tablespoons, of blood, though some women bleed more heavily. The OWH¹ puts the average at about two to three tablespoons.

If yours is heavier than that, see how to know if your period is too heavy.

How cycles change with age

The OWH¹ describes the pattern:

• Teens. Cycles longer than 38 days are common at first, and they typically settle within about three years.
• 20s and 30s. Cycles are usually regular and can last anywhere from 24 to 38 days.
• 40s. Cycles can become irregular. Periods can pause for a month or a few months and then return.

For what’s behind the 40s shift, see perimenopause.

What can make it irregular

The NHS³ lists puberty through menopause, along with pregnancy, hormonal contraception, significant weight changes, stress, excessive exercise, and conditions like PCOS or thyroid problems. It says irregular periods are not usually a sign of a problem, but that a medical evaluation helps determine the cause. See late or irregular periods, PCOS and spotting between periods.

Track it

The OWH¹ suggests recording your period’s start date, how long it lasts, how heavy it is, PMS symptoms, and any cramping or bleeding that affects your daily activities. It says apps can help you spot patterns. For the symptoms around your period, see PMS, PMDD and cramps.

The play

Try this: three months of cycle notes

For three cycles, write the first day of each period, the last day, how many pads or tampons you use on the heaviest day and any bleeding between periods.

Add pain, mood and sleep notes.

Count the days from the first day of one period to the first day of the next. That’s your cycle length. The range across three months is more useful than any single number.

When to get checked

The OWH¹ says to contact your healthcare provider if your cycles are consistently shorter than 24 days or longer than 38 days, or if you have severe pain or bleeding that causes you to miss regular activities. The NHS² says to see a GP for bleeding between periods, bleeding after sex, bleeding after the menopause, and any unexplained change to your usual cycle.

Book an appointment if any of these fit:

• Your cycles are consistently shorter than 24 or longer than 38 days
• Periods last beyond 7 days
• You have bleeding between periods, after sex or after menopause
• Your periods have stopped for several months and you’re not pregnant
• You have irregular periods alongside weight gain, fatigue or facial hair growth
• You’re trying to conceive and your cycle is unpredictable
• Pain or bleeding is making you miss work, school or life

Normal is a wide band, and your own pattern is the best baseline. A written record turns “something feels off” into a pattern a clinician can read.