What is the best time to have sex to conceive?

Optimal Timing for Conception

To maximize your chances of pregnancy, have intercourse during the 6-day window ending on the day of ovulation, with the highest probability of conception occurring when intercourse happens 1-2 days before ovulation. 1

The Fertile Window

The fertile window is approximately 6 days in each menstrual cycle, consisting of the 5 days leading up to ovulation plus the day of ovulation itself. 1, 2

• Conception is only possible during this 6-day period - intercourse outside this window will not result in pregnancy. 1
• The probability of conception increases as you approach ovulation, peaking at 33% on the day of ovulation itself. 1
• Intercourse 5 days before ovulation has approximately a 10% conception probability, which steadily increases each day closer to ovulation. 1
• The day before ovulation has the highest estimated probability of conception across multiple studies. 2
• After ovulation occurs, the probability of conception drops to essentially zero. 2

Timing Based on Cycle Length

Regular Cycles (26-32 days)

For women with regular menstrual cycles, the most fertile days are days 8-19 of the menstrual cycle (counting from the first day of menstrual bleeding as day 1). 3, 4

• In a typical 28-day cycle, ovulation usually occurs around day 14, making days 9-15 the critical fertile window. 4
• However, the timing of the fertile window varies greatly even among women with regular cycles, so relying on calendar calculations alone is insufficient. 3

Shorter Cycles (<26 days)

Women with shorter cycles experience earlier ovulation and an earlier fertile window. 4, 5

• For a 25-day cycle, the fertile period typically falls between days 6-11, with ovulation around days 11-12. 4, 5
• The fertile window shifts earlier proportionally as cycle length decreases. 5

Irregular Cycles

For women with cycles consistently outside the 26-32 day range, predicting the fertile window becomes more challenging and less reliable. 3

Recommended Strategy for Timing Intercourse

Use Ovulation Prediction Methods

Urinary ovulation predictor kits are the most evidence-based approach for timing intercourse to achieve pregnancy. 6

• These kits detect the luteinizing hormone (LH) surge that occurs 24-36 hours before ovulation. 4
• Using urinary ovulation tests increases the chance of live birth by approximately 36% compared to intercourse without ovulation prediction (from 16% to 22-28% per cycle). 6
• Urinary ovulation tests also probably increase overall pregnancy rates (clinical pregnancy or positive pregnancy test) by approximately 28%. 6

Practical Implementation

1. Begin testing several days before expected ovulation based on your typical cycle length. 4
2. When the LH surge is detected, have intercourse immediately and continue for the next 2-3 days. 4, 5
3. This approach ensures sperm are present throughout the fertile window, as sperm can survive up to 5 days in the female reproductive tract. 5, 7

Common Pitfalls to Avoid

Don't Rely on Day 14 Assumptions

Only 12.7% of women correctly estimate their actual ovulation day, with most women defaulting to day 14 or 15 regardless of their actual cycle. 8

• Among women trying to conceive, only 55% of estimated ovulation days fell within their actual fertile window. 8
• Only 27% of estimated ovulation days coincided with peak fertility days. 8
• The median error in self-estimation was 2 days, with a range of -10 to +27 days. 8

Fertility Awareness Methods Have Limited Evidence

While fertility awareness-based methods (tracking basal body temperature, cervical mucus, calendar apps) are options, the evidence is insufficient to determine whether they improve live birth rates compared to intercourse without ovulation prediction. 6

• These methods may be useful for anticipating ovulation by several days, particularly cervical mucus assessment. 2
• However, they have not been shown to reliably improve pregnancy outcomes in clinical trials. 6

Sperm and Egg Viability

Understanding the biology helps explain the timing recommendations:

• Sperm survival time averages 1.4 days, with a 5% probability of surviving more than 4.4 days and only 1% surviving beyond 6.8 days. 7
• Egg viability is approximately 0.7 days (less than 24 hours) after ovulation. 7
• This explains why the fertile window extends 5 days before ovulation but essentially ends on the day of ovulation itself. 7, 1

Age of Sperm and Pregnancy Viability

There is no evident relationship between the age of sperm and the viability of the pregnancy or the sex of the baby. 1

• Only 6% of pregnancies could be attributed to sperm that were 3 or more days old, but this reflects the lower probability of conception from earlier intercourse, not reduced viability. 1
• Cycles producing male and female babies showed similar patterns of intercourse timing relative to ovulation. 1