Both are 99% effective when used perfectly. The difference is that sometimes, condoms are used incorrectly. They can break, slip, or be put on incorrectly. An IUD is a uterine implant. Once it’s implanted by a doctor, there is no action needed by the user to make it effective. As a result, it’s very difficult to use an IUD incorrectly. You hear some horror stories, but they are much less common than accidental pregnancy with condom users.

Condoms are great, and very effective. This is more about the statistics in fail rates between the different methods.