Optimal Timing for Conception When Ovulation Occurs Today
If ovulation is occurring today, you should have unprotected intercourse today and ideally should have already had intercourse during the preceding 1-5 days for maximum conception probability. 1, 2
Understanding the Fertile Window
The fertile window spans approximately 6 days, ending on the day of ovulation itself. 3, 2 Research demonstrates that conception can only occur when intercourse takes place during the 5 days before ovulation through the day of ovulation. 2
The highest probability of conception occurs on the day before ovulation (33% per cycle) and the day of ovulation itself (also approximately 33% per cycle). 3, 2 The probability decreases progressively as you move further from ovulation:
- Day of ovulation: 33% conception probability 2
- 1 day before ovulation: 33% conception probability 3, 2
- 2 days before ovulation: ~27% conception probability 2
- 3 days before ovulation: ~16% conception probability 2
- 4 days before ovulation: ~13% conception probability 2
- 5 days before ovulation: ~10% conception probability 2
- After ovulation: essentially 0% conception probability 3, 2
Practical Recommendations for Today
Since ovulation is occurring today, you should:
- Have intercourse today (the day of ovulation) 1, 2
- Ideally, you would have also had intercourse yesterday and/or 2 days ago when conception probability was highest 3, 2
- If you haven't had intercourse in the past 5 days, having intercourse today still provides approximately 33% conception probability 2
Important Caveats About Ovulation Timing
Most women significantly misjudge their actual ovulation day. In one study of women trying to conceive, only 12.7% correctly estimated their ovulation day, with errors ranging from 10 days early to 27 days late. 4 The most common assumption (day 14) was frequently incorrect. 4
Even among women with regular cycles (26-32 days), the timing of the 6-day fertile window varies considerably between cycles. 5, 1 Unless you are using urinary LH detection kits or ultrasound monitoring, your estimate of "today is ovulation" may be inaccurate. 6
Sperm Survival Considerations
Sperm can survive in the female reproductive tract for an average of 1.4 days, with a 5% probability of surviving more than 4.4 days and a 1% probability of surviving more than 6.8 days. 7 This is why intercourse before ovulation is effective—sperm can wait for the egg. However, the egg itself only survives approximately 0.7 days (less than 24 hours) after ovulation. 7
This explains why intercourse after ovulation has essentially zero conception probability—the egg is no longer viable. 3, 2
Recommended Strategy for Future Cycles
For couples trying to conceive, the CDC recommends having intercourse every 1-2 days beginning soon after menstrual bleeding stops and continuing throughout the cycle. 1, 8 This approach ensures complete coverage of the fertile window without requiring precise ovulation prediction. 1
Alternatively, use urinary ovulation predictor kits to detect the LH surge (which occurs 24-36 hours before ovulation), then have intercourse when detected and continue for 2-3 days. 1, 8