How many days a month are you fertile?
You're fertile for about 6 days each cycle: the 5 days before ovulation and ovulation day itself. Sperm can survive up to about 5 days, while the egg lives only 12 to 24 hours. The chance of pregnancy is highest in the 2 days before ovulation and on ovulation day. Which calendar days these are varies from cycle to cycle.
Why about 6 days
Pregnancy needs a living sperm to meet a living egg. The egg survives about 12 to 24 hours after ovulation. Sperm can survive several days in fertile cervical mucus. Put together, that creates a window of about 6 days. A well-known study following 221 women found pregnancies came only from sex during the 6 days ending on ovulation day.
| Day relative to ovulation | Relative chance of pregnancy from sex that day |
|---|---|
| 5 days before | Low |
| 4 to 3 days before | Moderate |
| 2 days before | Highest |
| 1 day before | Highest |
| Ovulation day | High |
| The day after | Very low |
Which days of your cycle that is
Ovulation usually happens about 12 to 16 days before your next period. For a 28-day cycle, that's around day 14, making days 9 to 14 the likely fertile window. For a 35-day cycle, ovulation is nearer day 21, and the window shifts later.
But ovulation timing varies, even with regular cycles. In one study using hormone tests, only about 30% of women had their whole fertile window between days 10 and 17, and on every day from day 6 to day 21 there was at least a 10% chance of being in it. Our fertile window calculator gives an estimate from your cycle length, and what is the fertile window explains more.
Because the window moves, counting days is not a reliable way to avoid pregnancy, and Lulu is not contraception. If you're trying to conceive, sex every 2 to 3 days through the cycle means you don't need to time it perfectly.
How to narrow down your fertile days
- Cervical mucus: clear, slippery, stretchy mucus signals your most fertile days.
- LH tests: a positive means ovulation is likely within about 24 to 36 hours.
- Basal body temperature: a sustained rise shows ovulation has passed. See basal body temperature.
- Your own history: tracking several cycles shows your usual range.
Some people also notice their mood and energy peak in these days, as estrogen rises. See ovulation mood.
See a doctor if you've been trying to get pregnant for 12 months (6 months if you're 35 or older), if your cycles are very irregular or longer than 35 days, or if you have painful periods or known conditions such as PCOS or endometriosis.
Frequently asked questions
Can you get pregnant outside the fertile window?
Not if you know exactly when you ovulated, but you rarely do. That's why pregnancy sometimes happens on days that seemed safe.
How many days after your period are you fertile?
It depends on your cycle length. With short cycles, the fertile window can start right after your period. See how many days after period is ovulation.
What is the most fertile day?
The 2 days before ovulation and ovulation day itself have the highest chance of pregnancy.
Do you have fertile days if you don't ovulate?
No. Without ovulation there's no egg, so cycles without ovulation have no fertile window.
Sources
- Wilcox AJ et al. Timing of sexual intercourse in relation to ovulation. NEJM (1995)
- Wilcox AJ et al. The timing of the fertile window in the menstrual cycle. BMJ (2000)
- Cleveland Clinic: Ovulation
- 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.
How long does ovulation last?How long does ovulation last? The egg is released in moments and lives 12 to 24 hours, but the fertile window lasts about 6 days. Here's how it all fits.Ovulation calculator: when do I ovulate?Free ovulation calculator: enter your last period and cycle length to see your likely ovulation day for the next 4 cycles. Private, instant, estimates only.
Ovulation phase: signs, timing and feelingsThe ovulation phase explained: when you ovulate, how long it lasts, the signs and symptoms to look for, and why mood, energy and libido often peak.