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For example, what does it mean that condoms have a 2% to 15% failure rate? Another way to understand this is that condoms are 85% to 98% effective. The effectiveness rate is the opposite of the failure rate. Subtract the failure rate from 100, and that number is the birth control effectiveness rate. Condoms are 85% to 98% effective (meaning they have a failure rate of 2% to 15%).

This means that for every 100 women whose partners use condoms, from two to 15 of them will become pregnant within the first year of use. So basically, the failure rate does not refer to how many times you have sex, it correlates the number of people (100) who use that method over the course of one year. Failure rates refer to the number of pregnancies that take place when 100 women use that birth control method for one year