An egg loses its fertility within 24 hours

Sperm survive about a week — which is why the two days before ovulation, through the day itself, matter most.

An egg loses the ability to be fertilised about 24 hours after ovulation, while sperm survive around a week in the tubes. It is the sperm that waits. The fertile window runs from five days before ovulation to one day after, and peaks in the two days before through the day itself.