Is a 40-day cycle normal?
A 40-day cycle can be normal for teens, during perimenopause, while breastfeeding or after stopping the pill, and an occasional 40-day cycle happens to many adults. But for most adults a typical cycle is 21 to 35 days, so regular 40-day cycles are worth mentioning to a doctor. Common causes include PCOS, thyroid problems, stress and under-eating. In a 40-day cycle, ovulation is usually around day 26.
When a 40-day cycle is normal
| Situation | Is 40 days normal? |
|---|---|
| Teens, first few years of periods | Yes, cycles of 21 to 45 days are normal |
| Adults, once in a while | Usually fine; a late ovulation happens |
| Adults, most cycles | Outside the typical range; worth a check |
| Perimenopause (40s) | Common as ovulation becomes less regular |
| Breastfeeding or after birth | Common while hormones settle |
| After stopping hormonal contraception | Common for a few months |
Cycle length is counted from the first day of one period to the day before the next. See how long is a normal cycle for the full range, and our cycle length calculator to find your average.
When do you ovulate in a 40-day cycle?
The time from ovulation to your next period (the luteal phase) is usually about 12 to 14 days. So in a 40-day cycle, ovulation tends to happen around day 26 to 28, much later than the "day 14" you often hear. The long part is the follicular phase: it takes longer for an egg to mature and be released. If you're trying to conceive, ovulation tests or temperature tracking help pin it down.
Common causes of long cycles
- PCOS: irregular or delayed ovulation, often with acne, extra hair or weight changes. See PCOS.
- Stress, illness or travel: can delay ovulation for a cycle or two.
- Low energy: under-eating, weight loss or intense training. See can exercise delay your period.
- Thyroid conditions: both underactive and overactive thyroid can change cycles.
- High prolactin, sometimes from medication.
- Perimenopause: cycles often lengthen in the 40s.
Long cycles also change how PMS feels. With a long follicular phase, you might have more weeks of steady mood and energy, then a premenstrual stretch that seems to arrive out of nowhere because your period is "late". Tracking ovulation signs and mood makes those cycles easier to read. More in long menstrual cycle.
See a doctor if your cycles are regularly longer than 35 days (or 45 in the first years after your first period), if you have fewer than 9 periods a year, if you go 3 months without a period, or if long cycles come with acne, excess hair, weight changes or trouble conceiving. Take a pregnancy test if a cycle is unusually long for you and you could be pregnant.
Frequently asked questions
Can you get pregnant with a 40-day cycle?
Yes. You can still ovulate, just later. Long cycles mean fewer ovulations per year, so it can take longer, and a doctor can help if you've been trying for 6 to 12 months.
Is a 40-day cycle a sign of PCOS?
It can be, but not on its own. PCOS is diagnosed with a mix of irregular ovulation, signs of high androgens and ovary scans.
Is a 40-day cycle a sign of perimenopause?
In your 40s, cycles that start getting longer or more variable are one of the early signs. See first signs of perimenopause.
Sources
- ACOG: Menstruation in Girls and Adolescents: Using the Menstrual Cycle as a Vital Sign
- NHS: Irregular periods
- Bull JR et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine (2019)
- NHS: Polycystic ovary syndrome
This page is for information only and isn鈥檛 medical advice. If something worries you, please talk to a doctor.
Keep reading
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Cycle length calculator: is my cycle normal?Free cycle length calculator: enter the start dates of your last few periods to get your average cycle length and see whether your cycle counts as regular.
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