Long menstrual cycle: what it means if your cycle is over 35 days

When is a cycle "long"?

In adults, cycles from 21 to 35 days are considered normal. Longer than 35 days is called oligomenorrhea (infrequent periods), especially if it happens regularly or you have fewer than about eight periods a year. Teenagers are different: in the first few years after periods start, cycles up to about 45 days are common while ovulation settles.

Why cycles get long

The time from ovulation to your period, the luteal phase, is fairly fixed at around 12 to 14 days. So a 45-day cycle usually means ovulation around day 31 instead of day 14. Whatever delays ovulation stretches your cycle.

• PCOS (polycystic ovary syndrome), one of the most common causes of long cycles. Many people with PCOS have cycles over 35 days, often with acne, extra hair growth or weight changes.
• Stress, which can suppress the brain signals that trigger ovulation.
• Low energy availability: under-eating, significant weight loss or intense training.
• Thyroid problems and high prolactin.
• Coming off hormonal contraception, while your own cycle restarts. It can take a few months.
• Breastfeeding, which suppresses ovulation.
• The teenage years and perimenopause, when ovulation is less regular.
• Some medicines, including certain antipsychotics and steroids.

Long cycles and fertility

With long cycles you ovulate less often, so there are fewer chances to conceive each year, and timing is harder because day-14 estimates don't apply. Many people with long cycles still conceive. Watching for your own signs of ovulation helps a lot: egg white discharge, ovulation (LH) tests and a temperature rise. If you're trying to conceive and your cycles are regularly long, see a doctor early, as treatment to help ovulation is often simple.

Why long cycles are worth checking

If you rarely ovulate, the uterine lining is exposed to estrogen without regular progesterone to balance it. Over months to years, that can cause the lining to overgrow, which raises the risk of abnormal bleeding and, rarely, womb cancer. This is one reason doctors often recommend treatment that ensures a regular bleed, such as the pill or a hormonal IUD, when periods are very infrequent. Long cycles from PCOS can also be linked to insulin resistance, which is worth knowing about.

What helps

1. Track for three to six months: first day of each period and any signs of ovulation. Our cycle length calculator shows your average and range.
2. Take a pregnancy test if a cycle runs much longer than usual and pregnancy is possible.
3. Eat enough and recover well if you train hard or have lost weight.
4. Support your body with PCOS: regular activity and balanced meals can help cycles become more regular.
5. See a doctor for blood tests (thyroid, prolactin, androgens and others) and possibly an ultrasound.

Long cycles and mood

Long, unpredictable cycles can make PMS feel like it arrives from nowhere, and the long wait for a period often comes with worry about pregnancy or health. Many people find their mood still follows their own rhythm, with the harder days arriving in the two weeks after ovulation, whenever that happens. Logging mood alongside ovulation signs helps you see it. Read about irregular cycles tracking.