Sums things up? (4)
I believe the answer is:
adds
'sums things up?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for adds that I've seen before include "Puts (numbers) together" , "Aggregates or makes further remark" , "Counts" , "Contributes further" , "Reckons" .)