Ovulation tests and your fertile window

What is the fertile window?

Sperm can survive in the body for up to five days, while an egg survives for around 12 to 24 hours after ovulation. That makes your fertile window roughly six days: the five days before ovulation plus the day you ovulate.

How ovulation tests work

Ovulation tests measure luteinising hormone (LH) in your urine. LH rises sharply, known as the LH surge, usually 24 to 36 hours before ovulation. A positive test tells you ovulation is likely soon.

When to start testing

Ovulation usually happens around 14 days before your next period, not 14 days after your last one. For a 28-day cycle that is around day 14; for a 32-day cycle, around day 18. Start testing a few days before you expect to ovulate and test at the same time each day.

Cycle length	Likely ovulation day	Start testing around
26 days	Day 12	Day 9
28 days	Day 14	Day 11
30 days	Day 16	Day 13
32 days	Day 18	Day 15

Other signs of ovulation

• Cervical mucus becomes clearer, wetter and stretchier, like raw egg white.
• Basal body temperature rises slightly after ovulation, so it confirms ovulation rather than predicting it.

How Genesyx uses your results

Log each test in the Genesyx companion app and it shows your timing window for your chosen route, alongside your vaginal pH readings. See how timing differs for the XX and XY routes.

When to get advice

Speak to your GP if your cycles are very irregular, your tests never show a surge, or you have been trying to conceive for over a year (six months if you are over 35).