Count, calculate (6)
I believe the answer is:
reckon
This clue is a double definition.
'count' is the first definition.
(I know that count can be written as reckon)
'calculate' is the second definition.
(I know that calculate can be written as reckon)
(Other definitions for reckon that I've seen before include "Calculate, be of the opinion" , "what people who count will do" , "Have as opinion or count up" , "Conker (anag.)" , "Calculate roughly" .)