Irregular periods can make it harder to know when you ovulate, but many people with irregular cycles get pregnant naturally. Understanding the cause is the first step.
What is an irregular cycle?
For adults, a cycle is usually considered irregular if it is often shorter than 21 days or longer than 35 days, or if its length changes a lot from month to month. Occasional changes of a few days are normal.
Common causes
- Polycystic ovary syndrome (PCOS)
- Thyroid problems or a raised prolactin level
- Being underweight or overweight, or big changes in weight
- Stress, intense exercise or illness
- The years around puberty and perimenopause
- Stopping hormonal contraception: cycles can take a few months to settle
Finding your fertile days
Calendar predictions are less reliable with irregular cycles. These can help:
- Ovulation test kits, starting earlier in your cycle and testing for longer
- Cervical mucus: clear, stretchy mucus signals your fertile days
- Basal body temperature, to learn whether and when you ovulate
- Having sex every 2 to 3 days, so you do not need exact timing
When to see a doctor
- Your periods have stopped for 3 months or more and you are not pregnant
- Your cycles are usually longer than 35 days or shorter than 21 days
- You have been trying for 12 months (or 6 months if you are 35 or over)
Your doctor can check your hormones and thyroid, and may offer medicines that help you ovulate if needed.
Track your cycle with our Period Calculator and Fertile Window Calendar.