Reckon to make a hundred on the side - right? (8)
I believe the answer is:
consider
'reckon' is the definition.
(I know that reckon is a more specific form of the action consider)
'a hundred on the side right?' is the wordplay.
'a hundred' becomes 'C' (Roman numeral).
'right?' becomes 'r' (abbreviation).
'c'+'on'+'side'+'r'='CONSIDER'
'to make' is the link.
(Other definitions for consider that I've seen before include "Attend to" , "Think about, reflect upon" , "Look at someone or something thoughtfully" , "Take into account" , "Cogitate" .)