Birth-control pills work a lot better to prevent pregnancy than any of the other methods we have talked about. Much, much better than standing up. Much better than trying to pull out. Much better than restricting your activities to the hot tub. But the pill is not perfect either. Again, if there is a sperm and an egg involved, pregnancy is always a possibility.
In the course of a year, between 5 and 8 out of 100 women using the pill will have an accidental pregnancy. Those are better odds than for other methods (remember, it was 27 out of 100 women getting pregnant using the withdrawal method), but it’s not down to zero. Birth-control pills work best when a woman takes them every single day at the exact same time of day (especially if you are on an oestrogen-only pill). If you take the pills absolutely perfectly, you are even less likely to get pregnant. But if you are not good at taking a pill every day and at the same time every day, your chance of getting pregnant while using the pill is higher. Missing even one pill can significantly increase your chance of getting pregnant.