A vasectomy is one of the most effective forms of birth control, with an effectiveness rate of nearly 100% in preventing pregnancy once confirmed sperm clearance occurs

. However, it is not immediately effective; it typically takes about 3 months or 15 to 20 ejaculations for all sperm to be cleared from the semen

. During this time, additional contraception should be used to prevent pregnancy. After the procedure, a semen analysis is performed to confirm the absence of sperm. Once the sperm count reaches zero, the vasectomy is considered fully effective

. The failure rate is very low, with early failure rates (presence of motile sperm within 3 to 6 months) ranging from 0.3% to 9%, and late failure rates (after confirmed azoospermia) around 0.04% to 0.08%

. This failure rate is lower than that of other birth control methods such as condoms. Vasectomy is a permanent method of birth control designed to be a one-time procedure that provides lifelong contraception. While reversal is sometimes possible, it is not always successful and can be costly

. In summary, a vasectomy is over 99% effective at preventing pregnancy, making it one of the most reliable contraceptive methods available for people with penises and testicles