Although there are a number of days in the month when you are more fertile, there has not been a lot of high-quality research into whether timing sex around the 'fertility window' increases your chances of pregnancy. Having regular, unprotected sex every 2 to 3 days without contraception will give you the best chance of success. More than 9 out of 10 couples will get pregnant within two years. If you find that regular sex is too stressful or if you are unable to do it for other reasons, working out the time you are most likely to be fertile in the month makes sense. This is sometimes referred to as your 'fertile window' and there are various ways that you can work out when it happens for you.