FH-ADO-003 · ages 10-19

Why Are My Periods Irregular as a Teenager?

Growing Body & Preventive Health

If something feels unsafe or urgent

You can always get help, whatever your age, without an account.

Irregular periods are very common for the first two to three years after your first one. It usually means your hormones are still finding a rhythm.

What's happening

A cycle becomes regular once your body ovulates consistently, and that can take a couple of years. Stress, big weight changes, illness, heavy training and not eating enough can also delay or skip a period.

Usually normal

Cycles that vary by a week or two from month to month
Skipping the occasional month in your first two years
A period arriving late during exams or after being ill

Get checked if

No period for 3 months or more
Cycles shorter than 21 days or longer than 45 days after your third year
Irregular periods together with acne, extra facial or body hair, or weight change (this needs a PCOS check)
Any chance you could be pregnant

Your next step

Log three cycles in a row. If they are still outside 21 to 45 days, or a red flag matches, book a clinic visit and take your log.

Printable packs

My 10-19 Health and Independence Timeline
Organised Me: Weekly Health, School and Life Planner