Does the plan b pill always work ? i took it right after sex

Plan B : Plan b is very effective and usually works well.

Not ALWAYS.: It is not 100% effective. Plan B One-Step is up to 89 % effective when taken within 72 hours (3 days) after unprotected sex. It can reduce chance of pregnancy by up to 95% if used within 24 hours. It continues to reduce the risk of pregnancy up to 120 hours (5 days) after unprotected sex, but is less effective as time passes.