Tots up (4)
I believe the answer is:
adds
'tots up' is the definition.
('add' can be a synonym of 'tot up')
This is all the clue.
(Other definitions for adds that I've seen before include "Puts (numbers) together" , "Aggregates or makes further remark" , "Aggregates or appends" , "Goes on to say" , "Calculates the sum" .)