Fertile window: definition and meaning
The fertile window is the six-day stretch each menstrual cycle when sex can lead to pregnancy: the five days before ovulation and the day of ovulation. It exists because sperm can survive up to five days in fertile cervical mucus, while an egg lives only about 12 to 24 hours. The two days before ovulation carry the highest chance.
How it works in your cycle
| Day relative to ovulation | Approximate chance of pregnancy from sex that day |
|---|---|
| 5 days before | About 10% |
| 3 days before | About 15 to 25% |
| 2 days before | About 25 to 30% (highest) |
| 1 day before | About 25 to 30% |
| Ovulation day | About 10 to 15% |
| After ovulation | Very low |
Figures are approximate, from studies of couples trying to conceive. The window moves with your cycle: in a 28-day cycle it's around days 9 to 14, and in a 35-day cycle around days 16 to 21. Find yours with the fertile window calculator.
Why it matters
If you're trying to conceive, sex every one to two days through this window gives the best odds. Egg white cervical mucus and a positive ovulation predictor kit help pinpoint it. Many people feel more energetic and social now too, as estrogen peaks.
Calendar-based fertile window predictions are estimates. Ovulation can shift in any cycle, so they are not reliable contraception, and Lulu is not a contraceptive. If you need to avoid pregnancy, talk to a clinician about effective methods.
More detail in what is the fertile window and how many days are you fertile.
Frequently asked questions
Can you get pregnant outside the fertile window?
It's unlikely if you know exactly when you ovulated, but ovulation timing varies, so calendar predictions can be wrong.
How long is the fertile window?
About six days: the five days before ovulation plus ovulation day.
Sources
- Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. NEJM (1995)
- NHS: Fertility in the menstrual cycle
This page is for information only and isn鈥檛 medical advice. If something worries you, please talk to a doctor.
Keep reading
Fertile window calculator: when am I most fertile?Free fertile window calculator: see the days each cycle when pregnancy is most likely, for your next 4 cycles. Private, estimates only, not contraception.What is the fertile window?The fertile window is the 6 days ending on ovulation day when pregnancy is possible. How to estimate yours, the best days, and why it moves each cycle.
Ovulation: definition and meaningOvulation is when an ovary releases an egg, usually 12 to 14 days before your next period. Signs, timing, the fertile window, and how it affects mood.
What are "safe days"?"Safe days" are days of the cycle thought to carry a low chance of pregnancy. Why calendar-based safe days are unreliable, and what actually works.How many days a month are you fertile?How many days are you fertile? About 6 days each cycle: the 5 days before ovulation plus ovulation day. Which days are most fertile and why timing varies.