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What ovulation is
Ovulation is the moment an ovary releases a mature egg, which can then be fertilised over the next 12–24 hours. It usually happens around the middle of your cycle, and the days leading up to it are when you're most likely to conceive.
How this calculator works
In a typical cycle, ovulation occurs about 14 days before your next period starts. The calculator takes the first day of your last period and your average cycle length, estimates your ovulation day, and works out the fertile window and your next expected period around it.
Timing the fertile window
Because sperm can survive in the body for up to about five days, your fertile window opens several days before ovulation and closes about a day after. That gives roughly a six-day window each cycle — the calculator highlights it for you.
Signs of ovulation
Many people notice clear, stretchy cervical mucus, a slight rise in basal body temperature, mild one-sided pelvic twinges, or a heightened sense of smell around ovulation. Combining these signs with the calculator's estimate sharpens your timing. Planning further ahead? Pair this with our due date calculator.
Helpful tools
Detect the hormone surge that precedes ovulation.
View options →Chart the small temperature rise that confirms ovulation.
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Frequently asked questions
How accurate is an ovulation calculator?
It gives a good estimate for regular cycles, since ovulation is typically about 14 days before the next period. Irregular cycles reduce accuracy — ovulation kits or temperature tracking help.
How long is the fertile window?
About six days: the five days before ovulation plus ovulation day itself, because sperm can survive up to five days while the egg lasts around a day.
Can I use this for birth control?
No. Calendar estimates are not a reliable contraceptive method on their own. Speak to a healthcare provider about effective contraception.
What if my cycles are irregular?
The calendar method is less reliable with irregular cycles. Ovulation predictor kits, basal body temperature charting or talking to your provider give better guidance.