"Best Days of Your Life" is a song written and performed by American country artist Kellie Pickler, and co-written by Taylor Swift. It was released on December 1, 2008 as the second single from her self-titled second album. Swift also provides background vocals on the song. The song is about a narrator explaining how her former boyfriend cheated on her and moved on to a new girlfriend to start a family with, wishing them well on their new life but says that the new girl won't top what they previously once had before.

The song received negative reviews from critics who panned the lyricism and melody for being nondescript. "Best Days of Your Life" peaked at number 9 on the Billboard Hot Country Songs chart, Pickler's highest charting country single as of 2015. It also charted at number 46 on the Hot 100. The song was certified Platinum by the Recording Industry Association of America (RIAA), and has sold 1,133,000 units in the United States as of June 2010. The song also charted in Canada, peaking at number 99 on the Canadian Hot 100.

The accompanying music video for the song, directed by Roman White, features Pickler's ex-boyfriend having a miserable life with his new girlfriend and misses being with Pickler instead. Pickler debuted the song with a performance on November 12, 2008 at the 2008 CMA Awards. She also performed the song on American Idol, The Ellen DeGeneres Show, and the 2009 CMT Music Awards.

"Best Days of Your Life" is an up-tempo country pop song mostly backed by electric guitar. Its narrator tells about a former boyfriend who cheated on her and is going to get married and build a family with the lover. Although, she wishes them to be happy and have a nice life, she says that he's already had the best days of his life with her (the narrator), and the new partner can never top it.

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