Add up to, total (6)
I believe the answer is:
number
I believe this clue is a double definition.
'add up to' is the first definition.
(synonyms)
'total' is the second definition.
(I know that total is a kind of number)
(Other definitions for number that I've seen before include "Mathematical unit" , "less sensitive" , "Count - a digit?" , "Comparatively torpid" , "theme tune?" .)