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Late and irregular periods

There are many reasons your period might be late or irregular. While pregnancy is one reason, your lifestyle and medical factors can also be the cause.

On this page, we explain some of the most common reasons why periods can be late or irregular.  

What is an irregular period?

Regular periods start between 3 and 5 weeks from the start of the last period. An irregular period is when your period comes earlier or later than regular periods.  

Why is my period late/irregular?

Lifestyle Reasons

  • Stress - being stressed at home, at work, or in other areas of your life can affect your hormones and the part of the brain that controls your period (hypothalamus). Stress is the most common cause of irregular periods.
  • Weight loss or weight gain – sudden changes in your weight can change how your body functions, and can stop ovulation. This also applies to if you have an eating disorder such as anorexia or bulimia.
  • Too much exercise – if you exercise a lot, or you have increased the amount you exercise in a short space of time, your periods may stop.
  • Shift work – working evenings and nights can affect your internal biological clock and your period.
  • Travel – Going on holiday, especially traveling to different time zones, can affect your internal biological clock and most importantly, your hormones. Your period will likely go back to normal when your life goes back to normal.

Medical Reasons

  • Pregnancy – a late period is often an early sign of pregnancy. If you think there is a chance you might be pregnant, do a pregnancy test, or make an appointment at Family Planning or with your GP.
  • Polycystic Ovarian Syndrome (PCOS) – PCOS upsets your hormone levels. Small cysts can form on your ovaries which can lead to irregular ovulation (releasing of the eggs), or can stop it entirely. If you also notice other signs, such as more hair on your face and body, and worsening acne, you should make an appointment to talk to a doctor.
  • Early menopause – Menopause usually begins between 45 and 55. Early menopause is when women start to experience symptoms from 40, including missed periods.
  • Thyroid Issues – an overactive or underactive thyroid gland can cause late or irregular periods. Because the thyroid controls the body’s metabolism, hormone levels can also be affected.

If you only have three or four periods a year, or if you continue to have irregular periods, make an appointment to see a doctor at Family Planning or your GP.

Family Planning has clinics located throughout New Zealand. Use the clinic finder to find your nearest clinic.