Ovulation calculator: work out your fertile days
Estimate your fertile days using the first day of your last period and the length of your cycle. Free, no account required. Your input will not be saved.
Gain a better understanding of your cycle
Enter your details to get an estimate of your fertile days and your next period.
Your cycle may vary from month to month. A calculator cannot determine your ovulation. Do not use this calculation as a method of contraception.
How does this calculator work out your ovulation?
The calculator adds your cycle length to the first day of your last period. This gives an estimate of your next period. We then count back 14 days to estimate ovulation. The five days leading up to this and the estimated day of ovulation together form the fertile window shown.
This is a simplified calculation. Ovulation may occur earlier or later, even if your cycle is regular. Do not use this calculator to prevent pregnancy.
What can you do with the result?
You don’t need to know your exact ovulation date to get pregnant. Having sex every two to three days is usually enough to make the most of your fertile period. Read more about how often and when to have sex to get pregnant.
If your cycle varies significantly or you don’t know its length, this tool won’t provide any dates. Read how to recognise your ovulation and fertile days for other ways to understand your cycle. Consult your GP if your periods are irregular, have stopped, or if you have any concerns.
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