For the first two to three years after a first period, periods being uneven is the expected pattern rather than a problem. Gaps that are much longer or shorter than last time, a heavier month and then a light one, and a period that arrives nowhere near when you thought it would, are all ordinary at this stage. This page is health information for learning, and a doctor or a trusted adult can help with anything that worries you.

Why the first years are uneven

The cycle relies on hormones — chemical messengers — arriving in a particular order and amount. In the first years that system is still settling, so some cycles are longer, some shorter, and some months an egg is not released at all. That last part is why a gap can suddenly stretch.

None of this means your body is doing it wrong. It means it is early. Most cycles become steadier over the first few years [ACOG].

The range that is expected at this age

For teenagers, cycles anywhere from about 21 to 45 days apart are within the usual range [ACOG]. That is a much wider range than the "28 days" you see written everywhere, and the 28 is an average across adults rather than a rule.

A period itself usually lasts up to about 7 days [ACOG].

So a 24-day gap, then a 40-day gap, then a 33-day gap is not three problems. It is one ordinary teenage year.

"The app said Tuesday and it did not come. Is the app broken, or am I broken?"

Neither.

An app works out its guess from the cycles you have already logged. When those cycles vary — which is exactly what they are supposed to do right now — the honest answer is a wide range rather than a single day. Any app that shows you one confident date at this age is telling you something it does not actually know.

That is why Femio shows a window rather than a date, and why the window is wide for younger users. A wide window is the app being honest with you, not the app failing. There is more about this in tracking your cycle without stress.

You are not late. "Late" only makes sense against a date that was certain, and at this stage there is no certain date to be late against.

Things that are normal and often worry people

• Brown or dark blood, especially at the start or end. It is older blood; the colour is about time, not health.
• Small clots, the size of a small coin or less.
• Missing a month when you have been ill, under a lot of stress, sleeping badly, training very hard, or eating much less than usual.
• Feeling different each month — tired one period, fine the next.
• Spotting a day or two before it properly starts.

When to see a doctor

Most of what happens in these years needs nothing done about it. There is a short list where you or a trusted adult can arrange to see a doctor, and asking early is better than waiting to be sure.

You or a trusted adult can arrange an appointment if:

• you have not had a period by about 15, or by about three years after your breasts started developing
• your periods stop for more than about three months once they have started
• bleeding regularly soaks through a pad or tampon every hour or two, or lasts longer than 7 days
• pain stops you going to school or doing your usual things — see period pain in teens
• you bleed between periods, or after sex
• you often feel dizzy, breathless or very tired

A doctor will ask questions, and may suggest a simple blood test. In most cases the answer is that everything is settling normally. Nobody can tell what is going on from a list of symptoms on a phone, and this page is not trying to — it is telling you which things are worth a real appointment.

Seek care now: get help the same day if you are soaking through a pad or tampon every hour or two for several hours, if you faint or nearly faint, if you have pain you cannot function through, or if you feel very unwell with a fever while using a tampon — take the tampon out first.

If it is hard to raise any of this at home, there are other adults who can help you. If you want the basics again from the start, what is a period covers them.