ovulation calculator and calendar
Use our ovulation calculator to find the most fertile days in your cycle. Knowing which days you are most fertile can increase your chances of getting pregnant - our ovulation calendar will outline these days for you. This tool works best for those with a regular menstrual cycle.
Find your most fertile days
Select the first day of your Last Menstrual Period (LMP)
How are my most fertile days calculated?
You are at your most fertile in the five days leading up to and including ovulation. These five days are called your fertile window. Your fertile window is calculated using the date of the first day of your last menstrual period and combining it with the usual number of days in your menstrual cycle. From this you can work out the day you will ovulate.
Once you know when you will ovulate you can calculate which days you will be at your most fertile.
You can only get pregnant within those five days.
That's because sperm only has a lifespan of about 5 days and the lifespan of the ovum is only 24 hours. So if you have sex 6 days before ovulation your chance of falling pregnant is almost nil. The sperm will not live long enough to fertilise the egg when it is released on ovulation. If you have sex 5 days before ovulation then your chance is slightly greater and it increases each day as ovulation grows nearer.
At the end of your fertile window your chances of falling pregnant drop rapidly. If you have sex 24 hours after ovulation it is very unlikely that you will conceive.
More ovulation and fertility resources