"Mileage" (마일리지; Mailliji) is a song by South Korean musicians Jung Yong-hwa of CNBLUE and Yang Dong-geun (YDG). Released on January 9, 2015, it serves as the pre-release single of the former's debut solo studio album One Fine Day (2015). While filming for the television series The Three Musketeers (2014), Jung was inspired by YDG's affection towards him family on set to compose the song. Upon release of Jung's album, the two performed "Mileage" on music programs and talk shows. The song debuted and peaked at number 57 on South Korea's national Gaon Digital Chart, selling over 78,000 digital downloads since its release.

In May 2014, Jung was in talks to take part in TVN's television series The Three Musketeers. He was officially cast the following month and would star alongside actors Lee Jin-wook and Yang Dong-geun. As recording for the series took place, Yang conveyed endearment to his family on set; Jung took this as inspiration to write the melody for "Mileage". After listening to the track, Yang immediately wrote his rap. He stated that "it formed connections in my head right away", further expressing that that Jung was a "musician who has overcome genres".

"Mileage" was written and composed by Jung; YDG contributed the lyrics of his rap. The song is composed in the key of E major using common time with a tempo of 90 beats per minute.

On January 6, 2015, FNC Entertainment's homepage was redesigned into a teaser website for One Fine Day. The following day, it was revealed that Jung had collaborated with YDG on the track "Mileage". It serves as a pre-release single to the album. One day prior to its release, a music video teaser for "Mileage" was revealed; the full version was uploaded on January 9. It features the duo dressed in hip hop apparel with "cartoon-esque" imagery, along with "comical, straight-faced acting".

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