add up . add up {v.} 1. To come to the correct amount. The numbers wouldn't add up. 2. {informal} To make sense; be understandable. His story didn't add up. Categories: add yours {informal} {v.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2024 To section: A Subscribe to: American IdiomsIdioms feedEnglish languageHome page and general feed Leave my opinion