Understanding your most fertile time
What is a fertile window?
Your fertile window refers to the most fertile days in your menstrual cycle which give you the highest chance of conceiving. If you are trying to fall pregnant, the timing of when you and your partner have sex is critical.
Your fertile days are the five days before ovulation, through to the day of ovulation.
These six days are known as your ‘fertile window’, and are technically the only time in your cycle you can become pregnant.
Approaching the day of ovulation, your chances of conceiving increase. So if you have sex six or more days before you ovulate, it is very unlikely you would conceive.
The next day, your probability will have increased a little – to about ten per cent. And for the next few days, the chance will increase steadily, until the two days before ovulation, and the day of ovulation.
To work out your fertile window, you need to know your cycle length. This is calculated from day 1, being the first day of your period, until the next day 1. Once you know your cycle length, you can work out your likely ovulation day.
Ovulation day is 14 days before your expected period. In a 28 day cycle, this will be day 14 but in a 35 day cycle, ovulation day will be day 21. Now you can work out your fertile window because it will start 5 days before your ovulation day and finish the day after ovulation day.
If you have sex on any of these three days, your chance of pregnancy is about 30 per cent, in a normally fertile woman. Once you know your fertile window, you should have sex at least every two days during this time for the best chance of conception.
In the 12 to 24 hours following ovulation, your fertile window quickly closes and it becomes unlikely for you to fall pregnant during that cycle.
If you are not sure about when your fertile window is, we help you to track your cycle, and sometimes this is all that is needed for a couple to conceive naturally.