Fertile window calculator: when am I most fertile?
Fertile window: Sun, Oct 25 – Sat, Oct 31
- Fertile Sun, Oct 25 – Sat, Oct 31 · ovulation ~Fri, Oct 30
- Fertile Sun, Nov 22 – Sat, Nov 28 · ovulation ~Fri, Nov 27
- Fertile Sun, Dec 20 – Sat, Dec 26 · ovulation ~Fri, Dec 25
- Fertile Sun, Jan 17 – Sat, Jan 23 · ovulation ~Fri, Jan 22
🔒 Calculated in your browser. Nothing you type is sent or stored. Estimates only: cycles vary.
Your fertile window is the five days before ovulation plus ovulation day itself, because sperm can survive for several days but an egg lives for only about a day. The calculator estimates ovulation as 14 days before your next period, then marks the five days before it through the day after. Your most fertile days are usually the two or three before ovulation.
How the fertile window is calculated
Two facts set the size of the window. Sperm can live for up to 5 days (sometimes longer) in fertile cervical mucus, and an egg survives for only about 12 to 24 hours after it's released. So sex in the days before ovulation can lead to pregnancy, but sex a day or two after it usually can't.
The calculator first estimates your ovulation day by counting 14 days back from your next expected period. It then marks the five days before ovulation, ovulation day and the day after, a seven-day band that gives a little room for error. You'll see this for your next four cycles, with the current one colored on the mini calendar.
A calendar window is not a method of contraception and can't tell you which days are safe. Your dates are calculated in your browser and never sent anywhere.
Which days are most fertile?
Not every day in the window carries the same chance. In the landmark study of couples trying to conceive, pregnancy happened only when sex fell in the six days ending on ovulation day, and the chance was highest in the last two or three of them.
| Day relative to ovulation | Chance of pregnancy from sex that day (approx.) |
|---|---|
| 5 days before | about 10% |
| 4 days before | about 16% |
| 3 days before | about 14% |
| 2 days before | about 27% |
| 1 day before | about 31% |
| Ovulation day | about 33% |
| 1 day after | very low |
Those figures come from healthy couples in a research study, so treat them as a shape, not a promise. Age, sperm health and many other things change the real numbers.
Why your fertile window moves
The window follows ovulation, and ovulation is the part of the cycle that shifts most. A research team at the US National Institutes of Health found that only about 30% of women had their fertile window entirely within days 10 to 17, the days many guides assume. Some were fertile as early as day 6, others well past day 20. Teens, people after pregnancy and people in perimenopause vary even more.
- Watch your body too: slippery, egg-white discharge and a positive LH test both point to the most fertile days. See signs of ovulation.
- Track a few cycles: your real range matters more than one average. The cycle length calculator shows how much yours varies.
- Notice your mood: many people feel brighter, more social and more interested in sex in the fertile window, as estrogen peaks. It's one of the easier patterns to spot.
When to talk to a doctor
If you've been trying to get pregnant for a year (or 6 months if you're 35 or older), see a doctor; sooner if your periods are very irregular, very painful or have stopped. If you want to avoid pregnancy, ask a doctor, nurse or pharmacist about contraception: calendar counting alone is unreliable.
Frequently asked questions
How many days are you fertile each month?
About six: the five days before ovulation and ovulation day. Calculators often show seven to allow for error. Read more in how many days are you fertile.
Can you get pregnant outside your fertile window?
If the window is estimated from a calendar, yes, because ovulation can come earlier or later than predicted. Pregnancy from sex well after ovulation is very unlikely.
Is the fertile window the same as ovulation?
No. Ovulation is the single moment an egg is released. The fertile window is the stretch of days before it when sex can lead to pregnancy.
Can I get pregnant on my period?
It's unlikely but possible, especially with short cycles, because sperm can survive until an early ovulation. See can you get pregnant on your period.
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)
- NHS: Fertility in the menstrual cycle
- Cleveland Clinic: Ovulation
This page is for information only and isn’t medical advice. If something worries you, please talk to a doctor.
Keep reading
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.
Safe days calculator: why calendar safe days can't prevent pregnancyLooking for a safe days calculator? Here's why calendar safe days are unreliable as contraception, what the numbers say, and what works instead.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 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.Can you get pregnant on your period?Can you get pregnant on your period? It's possible but less likely. How sperm survival and early ovulation make it happen, with the real numbers.