Calculate Your Fertile Window with Our Ovulation Tool
If you're trying to conceive, knowing when you ovulate can help you spot your most fertile days. Our ovulation calculator uses your cycle length and the first day of your last period to estimate when ovulation is most likely to happen.
What is ovulation?
Ovulation is when one of your ovaries releases an egg, usually around 14 days before your next period. For people with regular cycles, this can make it easier to estimate the best time to try for a baby.
Sperm can survive inside the body for up to five days, while an egg is usually viable for around 12 to 24 hours. That is why your fertile window includes the days leading up to ovulation, not just ovulation day itself.
How this calculator works
The calculator estimates your likely ovulation day by subtracting your luteal phase length from your average cycle length. It then shows your fertile window and a possible due date if conception happened in that cycle.
What can affect the prediction?
Your luteal phase
The luteal phase is the time between ovulation and your next period. For many people it is around 14 days, but it can vary. If you know your usual luteal phase length, adding it here can make the estimate more personal.
Cycle length changes
If your periods are irregular, ovulation can happen earlier or later than expected. This tool is still useful as a guide, but signs like cervical mucus, temperature tracking, and ovulation tests may give you a clearer picture.
When is the best time to have sex to conceive?
Your fertility window usually covers the few days before ovulation and ovulation day itself. Trying during this window gives you the best chance of conception.
This calculator is a helpful guide, but it is not a medical tool. Ovulation can shift from cycle to cycle, even when periods are usually regular. If you have concerns about your cycle or fertility, speak to your GP or fertility specialist.