Lambert topped the chart of the reality singing competition's top-earning contestants for the first time last year considering he raked in a career-high of $10 million, a significant portion of which accumulated from his gig as the rock band Queen's frontman.
"Adam used the launching pad of American Idol very well to have a successful recording career," Lambert's co-manager Martin Kirkup previously told Forbes.
Although Season 4 winner Underwood grossed the most money in 2013 and 2014 out of all Idol's artists, she finished in second place last year. The country superstar reportedly earned $8 million thanks to her records and live performances. She'll also be kicking off her latest "Storyteller Tour" at the end of January.
Lambert also beat out fifth-season finalist Chris Daughtry, who was ranked third based on his $6 million income. Daughtry and his band took on 91 shows in 2015. Fourth place went to Season 11 winner Phillip Phillips with approximately $5 million because he cashed in on 83 concerts stemming from his 2014 album Behind The Light, according to Forbes.
Idol's Season 1 winner Clarkson and Season 10 winner Scott McCreery tied for fifth place. Both artists earned around $4 million last year, but it was apparently a "down" year for Clarkson in terms of touring so her number is still quite impressive. McCreery reportedly played 55 concerts in 2015.
Forbes compiled this "scoring" list based on pretax earnings from June 2014 to June 2015.