The fertile window, and why most timing advice is wrong
Six days, ending on the day of ovulation. Everything after that is noise.
In the study that settled this, conception occurred only when intercourse took place during a six-day period ending on the estimated day of ovulation. Not before it, not after it.
Within that window the chance rises steadily: about 10% five days before ovulation, about 33% on the day itself. A separate analysis of family planning cohorts put the peak one day earlier. The two do not fully agree on the single best day, which is a good reason to think about the window rather than about one date.
- The fertile window is
the 6-day interval ending on the day of ovulation.
- Intercourse every one to two days in that window gives the highest rates, but two to three times a week is
nearly equivalent.
Couples should not be advised to limit the frequency of intercourse when trying to achieve pregnancy.
Specific coital positions and postcoital routines have no impact on fertility.
Two other findings from the same study, because they come up: sperm age had no evident relation to whether the pregnancy survived, and the timing of intercourse relative to ovulation had no influence on the sex of the baby.
One thing the window does not do is get shorter as you get older. The daily-records study looked specifically and found no evidence for that in either partner. Older couples have a less fertile window, not a narrower one.