Period calendar: predict your next period

Knowing when your period is due means fewer surprises and more peace of mind. Here’s how the calculation works, and what’s normal or not.

How a cycle is counted

A cycle starts on the first day of your period (day 1) and ends the day before your next period. To find your cycle length, count the days between two first days of bleeding.

People often say 28 days, but that’s an average: in adults, a cycle of 21 to 35 days is considered usual. In your teens, and in the years before menopause, cycles can vary more.

Predicting the date of your next period

The simplest method: take the average length of your last few cycles and add it to the first day of your last period. The more cycles you log, the more accurate the estimate. A difference of a few days from one month to the next is common: stress, travel, illness or a change of routine can shift your period.

How long does a period last?

A period usually lasts 3 to 7 days, generally with one or two heavier days at the start. Logging your flow day by day helps you see what’s usual for you.

When to talk to a doctor

• Your cycles are regularly shorter than 21 days or longer than 35 days.
• You haven’t had a period for 3 months (outside pregnancy, breastfeeding or contraception that stops periods).
• Your period lasts more than 7 days or is so heavy you need to change your protection every hour.
• You bleed between periods or after sex.

Ragnagna is not a medical device and does not replace advice from a health professional. If in doubt, talk to your doctor, midwife or gynaecologist.