Why is withdrawal less reliable than some other birth control methods?

Coitus interruptus, or the withdrawal method, is considered less reliable than many other forms of birth control primarily because it does not account for drops of seminal fluid that may be released before ejaculation occurs.1

While the method can be effective when performed perfectly, its reliability is significantly lower in typical use. The failure rate for withdrawal is approximately 4 percent when practiced correctly, but it rises to more than 20 percent with typical use. This variability makes it less predictable than highly effective, consistent methods such as hormonal contraceptives or intrauterine devices, which can achieve success rates of approximately 99 percent.21