When is the fertile window?
About six days: the five days before ovulation, plus ovulation day itself.1 Ovulation doesn’t happen on the same day for everyone, so those six days move around too.2
What the studies found
In a study that followed 221 women who were trying to conceive, with hormones measured in daily urine samples, conception happened only after sex during a six-day window that ended on the estimated day of ovulation.1
Day 14 is an average, not a rule
The researchers also found that the timing could be unpredictable, even for people whose cycles were usually regular.2
What a temperature chart can tell you
After ovulation, resting (basal body) temperature typically rises about 0.3 to 0.6 °C and stays up until the next period.3 So a temperature chart can suggest that ovulation happened, after the fact. It can’t predict it.3
In practice
The days leading up to ovulation matter most. If your cycles are irregular, or you’ve been trying for a while, that’s worth bringing to a visit.
General information, not medical advice for you. Bring questions about your own health to a visit with any clinician you trust.