What is my fertility window?

Your "fertility window" also known as the "fertile window" consists of the 5-6 fertile days of your menstrual cycle 4-5 days before and the day of ovulation when intercourse is most likely to result in pregnancy. This fertile window starting 5 days before the day of ovulation until the day of ovulation. Your most fertile of these days are the 2 days before plus the day of ovulation.

Making love 24+ hours after the day of established ovulation is unlikely to improve your chances of getting pregnant.

On which days of my menstrual cycle am I more likely to get pregnant?

The 2 days before ovulation plus the day of ovulation have the highest chance of getting you pregnant if you have intercourse only once during the fertility window.

These 3 days are the best fertility window:

Best Fertility Window

Applies to intercourse for only one day. 

  • 6 days before ovulation (-6 dpo) : 0 %
  • 5 days before ovulation (-5 dpo) : 8 %
  • 4 days before ovulation (-4 dpo) : 17 % 
  • 3 days before ovulation (-3 dpo) : 8 %
  • 2 days before ovulation (-2 dpo) : 36 %
  • 1 day before ovulation (-1 dpo) : 34 %
  • The day of ovulation (dpo) : 36 %
  • Any day (24+ hours) after ovulation: (1+ dpo) : 0%

Adapted from Wilcox, AJ. et al. NEJM (1995)

Wilcox NEJM 1999

Why can I get pregnant from intercourse 5 days before ovulation?

Increasing amounts of estrogen in the cervical mucus and reproductive tract of a woman approaching ovulation generally allows the sperm to live for up to 6 days in the woman's uterus.

Does the timing of intercourse help?

Studies have shown that even in women with regular cycles, ovulation can possibly happen any time, so "timing" of intercourse has never been shown to improve your pregnancy chances. You are probably not improving your chances of getting pregnant if you wait for intercourse until the temperature goes up or the OPK has become positive. You may already have ovulated by that time, and sex after ovulation is unlikely to get you pregnant.

Every day or every other day intercourse?

Couples who tried to get pregnant were previously told to have sex once every other day during their fertile days. Recent studies have shown that the average couple who is trying to conceive should make love regularly 2-3 times a week, every week because you don't know exactly when ovulation happens.

In addition, you may improve your chances if you have sex once a day (as long as his sperm are OK) during the fertile 4-5 days prior to, and the day of, ovulation. In those rare circumstances when the man does not have enough sperm (oligospermia), the old rule of once every other day still holds true.

  • Sex every day: 37% chance of pregnancy
  • Sex every other day: 33%  chance of pregnancy
  • Sex once a week: 15%  chance of pregnancy

From: "Timing of Sexual Intercourse in Relation to Ovulation -- Effects on the Probability of Conception, Survival of the Pregnancy, and Sex of the Baby" was published in The New England Journal of Medicine (December 7, 1995 -- Vol. 333, No. 23). Allen J. Wilcox, Clarice R. Weinberg, Donna D. Bair