Success rate if i practice the rhythm method of birth control?

Success of rhythm: If you know your own body and can check your own cervical mucus rhythm works fairly well as a contraceptive method. Avoid have sex 4 days before you expect to ovulate until 2 days after ovulation. Sperm can survive in the female tract for 3 days, and the egg is can be fertilized for 24 hrs after ovulation. As long as you accept abortion as a fail safe, you should be fine.