The timing of ovulation varies according to your cycle length, so to find out when youâre most fertile, you need to know your own body and cycle. You can work out the length of your cycle by counting from the first day of your period (Day 1) to the day before your next period starts. Ideally youâll have this information before you start using an ovulation test.
Cycle lengths differ from woman to woman and cycle to cycle but are usually between 23 and 35 days long.