Requirements for proving primary residence 2 of 5 years

[Michael Sandvig]

hi all! looking for some guidance here. what proof does the IRS require to show that you lived in the home as your primary residence for 2 of 5 years? example: I bought a townhome in aug 2015, lived in it for just over a year until oct 2016 and began renting it out until moving back in feb 2018, treating as my primary residence for another year, until feb 2019 - if i sell before aug 2020 do i qualify for the capital gains exemption?