A released egg only survives for 24 hours which provides a very narrow window for intercourse, the good news is you have more fertile days, as getting pregnant doesn’t just rely on the lifetime of the egg but also the lifetime of the sperm. Sperm can survive in your body for about 5 days after sex. So you can still conceive even if you have sex 4 – 5 days before ovulation which allows more flexibility to get together and plan intercourse around everyday life.

The day before ovulation and the day of ovulation are known as your peak fertility days. An ovulation test detects an increase in oestradiol (a form of oestrogen) prior to an LH surge (Luteinising Hormone) which happens 24-36 hours before ovulation so you can more accurately identify your fertile window. 

The average menstrual cycle is 28 days long and ovulation usually occurs on day 14 but all women are unique and research suggests that nearly 50% of a woman’s’ cycle vary by 7 days or more, if menstrual cycles vary in length so does ovulation which can make it difficult to know when your fertile window is.

The timing of ovulation can vary by a day or two even in the most regular of cycles.

An ovulation calculator estimates how likely you are to release an egg on a particular day and can help you identify your most fertile days. 

The calculator works by taking the first day of your last period and the length of your menstrual cycle to give you a range of days when you may release an egg.

The ovulation calculator is for information purposes and may give you an understanding of your fertility window, but it is by no means a substitute for understanding what is going on in your body.

Ovulation Calculator
When did your last period start?
E.g. 18/01/2020
Usually, how long is your cycle?
Cycles typically vary from 23 to 35 days
Estimate your ovulation day
likelihood of ovulating today
Due to your cycle length, unfortunately we can't estimate an ovulation probability. We recommend that you use a Digital Ovulation Test to accurately detect your most fertile days.
Start of your last period
Likelihood of ovulating on this date
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In partnership with Clearblue®.
Results are based on the information you have provided and data from the publication below: Sarah Johnson, Lorrae Marriott & Michael Zinaman (2018): “Can apps and calendar methods predict ovulation with accuracy?”, Current Medical Research and Opinion, DOI:10.1080/03007995.2018.1475348