1
general::
1. Amount to an expected or correct total, as in These figures don't add up, meaning they are not correct. [Mid-1800s] 2. Be consistent, make sense, as in I'm not sure that all this testimony will add up. [First half of 1900s] 3. Assess, form an opinion of, as in He looked across the track and added up the competition. Also see ADD UP TO.
American Heritage Idioms
2
general::
Phrase(s): add something up
to sum or total a set of figures. (See also add up (to something).) • Please add these figures up again. • I didn’t add up these figures!, Phrase(s): add up (to something)
1. Lit. [for a set of figures] to equal a total. • These figures don’t add up to the right total! 2. Fig. [for facts or explanations] to make sense. (Considering facts as if they were figures.) • Your explanation just doesn’t add up!
McGrawhill's American Idioms And Phrasal Verbs