If your cycle shifts a little from month to month, that's normal: for the same person, cycle length varies by 2–3 days on average. In adults a cycle is often 21–35 days long. Doctors start looking into it when cycle length jumps around by more than 7–9 days or falls outside that range.
Why does my cycle change?
Cycle length depends mostly on when you ovulate, meaning when an egg is released from the ovary. From ovulation to your period is about 10–16 days, but the first half of the cycle can stretch or shrink. Some cycles have no ovulation at all, and then periods come unpredictably, sometimes heavier than usual.
What throws a cycle off?
Common causes are stress and anxiety, losing or gaining a lot of weight, and too much exercise. Hormonal contraception can change the rhythm too: the progestogen-only pill, the injection, a hormonal coil.
Sometimes the cause is PCOS or a thyroid problem. And a missed period is often an early sign of pregnancy, so take a test if you could be pregnant.
What can I do if my cycle is off?
Irregular periods usually aren't a sign of a problem, and they don't always need treatment. Start by keeping notes: the first day of each period, how many days it lasted and how heavy it was. After 3–6 months, the app will show your real range.
If stress, dieting or hard training threw your cycle off, sleep, proper meals and easing off exercise can help bring the rhythm back. A doctor will ask about your cycles, weight, exercise and medicines, and may suggest blood tests or an ultrasound. With notes on your phone, you won't have to remember dates on the spot.
Common questions
My cycle is 23 days. Is that too short?
No. A regular cycle of 21 to 35 days is normal, and 23 fits right in. In a study of over 600,000 cycles, only one in eight was exactly 28 days.
Can I get pregnant if my cycle is irregular?
Yes. With an irregular cycle you may ovulate less often and on different days, so it can take longer, but it doesn't protect you from pregnancy. If you're trying for a baby, it can help to have sex every 2–3 days throughout your cycle.
I stopped contraception and my cycle hasn't settled. Is that common?
After the injection, yes: periods can take a few months to get back to normal. After the combined pill, fertility usually returns in about a month, so if your cycle stays off for a long time, show it to a doctor. Either way, you can get pregnant before your first period, so use contraception straight away if you're not planning a baby.
In short
- Log the first day of every period
- Could you be pregnant? Take a test first
- Show your doctor your cycle history from the app
Source: NHS: Irregular periods
Educational content; it does not replace professional medical advice.