go an extra mile

go the/an extra mile (to make more effort than is expected of you) — сделать больше, чем ожидалось, превзойти себя; выложиться полностью; выполнить и перевыполнить

Example 1: He's a nice guy, always ready to go the extra mile for his friends. — (CIDI)

Example 2: He's always willing to go the extra mile to do things right. (Cambridge Dictionary of American Idioms)

Example 3: Amanda's a hard worker and always goes the extra mile.

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"Going the extra mile" means that you have gone above and beyond what was required of you. This originates from Jesus' Sermon on the Mount, when He said, "Whoever forces you to go one mile with you, go with him two." Thus, you are fulfilling Jesus' commands by "going the extra mile" beyond what is required. (Mt 5:41)

see also
[bend over backwards]