I have a mirena iud but i'm constantly hearing about pregnancy's still happening with them. is that the .o1 percent reporting? do i always need backu?

Mirena failure rate: "The failure rate of Mirena is approximately 0.2% in the first year and the cumulative failure rate is 0.7% after 5 years." Please see: https://www.mirena-us.com/q-and-a/ Most women don't feel the need to use backup with Mirena. Although nothing is absolutely 100% effective - Mirena is really pretty dog-gone effective. In answere to your question - You don't need to use backup.