Ovulation calculator for a 27-day cycle
Ovulation ~Thursday, October 29 · fertile Sat, Oct 24 – Fri, Oct 30
Ovulation ~Wednesday, November 25 · fertile Fri, Nov 20 – Thu, Nov 26
Ovulation ~Tuesday, December 22 · fertile Thu, Dec 17 – Wed, Dec 23
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With a 27-day cycle, you most likely ovulate around cycle day 13 (day 1 is the first day of your period). Your fertile window is roughly days 8 to 14, and your best chance of conceiving is from day 11 to day 13. Enter your last period above to turn that into dates.
When do you ovulate with a 27-day cycle?
Ovulation usually happens about 14 days before your next period, not 14 days after the last one. The part of the cycle after ovulation, the luteal phase, is fairly steady at 12 to 14 days for most people, while the part before it stretches or shrinks. So with a 27-day cycle you count back 14 days from day 28 (the first day of your next period) and land on day 13.
| Cycle day | What usually happens in a 27-day cycle |
|---|---|
| 1 to 5 | Your period (most people bleed 3 to 7 days) |
| 6 to 7 | Follicular phase: estrogen rises, energy and mood usually lift |
| 8 to 12 | Fertile window opens: sperm can survive up to 5 days |
| 13 | Estimated ovulation, the most fertile day along with the 2 days before |
| 14 to 27 | Luteal phase: progesterone rises; PMS often shows up in the last week |
Your fertile window with a 27-day cycle
An egg lives for about 12 to 24 hours after ovulation, but sperm can survive up to five days. That makes days 8 to 14 your fertile window, with the highest chances on days 11, 12 and 13. In the classic study of couples trying to conceive, sex on the two days before ovulation and on ovulation day itself carried the highest chance, about 27 to 33% per cycle.
With a 27-day cycle, start daily ovulation (LH) tests on cycle day 11, about 17 days before your next period is due, and keep going until you get a positive. Ovulation usually follows 24 to 36 hours later. See our ovulation test calculator.
Is a 27-day cycle normal?
A 27-day cycle is right in the middle of the normal range (21 to 35 days). Large app studies put the average cycle at about 29 days, so 27 days is as normal as 28.
Cycles also vary from month to month. If yours swing by several days, use the dates as a starting point and check signs of ovulation such as stretchy, clear discharge or a positive LH test. Our ovulation calculator for irregular periods works from your last few cycles instead of a single number.
27-day cycle compared with other cycle lengths
| Cycle length | Likely ovulation day | Fertile window |
|---|---|---|
| 23 days | day 9 | days 4 to 10 |
| 25 days | day 11 | days 6 to 12 |
| 27 days (yours) | day 13 | days 8 to 14 |
| 29 days | day 15 | days 10 to 16 |
| 31 days | day 17 | days 12 to 18 |
Calendar dates are estimates and are not a method of contraception. See a doctor if your cycles are often shorter than 21 or longer than 35 days, if periods stop for 3 months, or if you've been trying to conceive for 12 months (6 months if you're 35 or older).
Frequently asked questions
What day do I ovulate on a 27-day cycle?
Most likely around day 13, counting the first day of your period as day 1. It can move a day or two either way from cycle to cycle.
When is the best time to try to conceive with a 27-day cycle?
Have sex every 1 to 2 days from about day 8 to day 14, with the most fertile days being 11 to 13.
Can I get pregnant right after my period with a 27-day cycle?
It's less likely but possible: your fertile window usually opens around day 8, and sperm can survive up to five days, so an early ovulation or a long period could overlap.
When should I take a pregnancy test with a 27-day cycle?
From the day your period is due, day 28, for an accurate result. Use our pregnancy test calculator for the exact date.
Sources
- Wilcox AJ et al. Timing of sexual intercourse in relation to ovulation. NEJM (1995)
- Bull JR et al. Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. npj Digital Medicine (2019)
- NHS: Periods and fertility in the menstrual cycle
- ACOG: Evaluating Infertility FAQ
This page is for information only and isn’t medical advice. If something worries you, please talk to a doctor.
Keep reading
Ovulation calculator for a 25-day cycleWith a 25-day cycle you usually ovulate around day 11, fertile days 6 to 12. See your exact dates for the next three cycles, free.Ovulation calculator for a 26-day cycleWith a 26-day cycle you usually ovulate around day 12, fertile days 7 to 13. See your exact dates for the next three cycles, free.
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