Calculates – or guesses (7)

I believe the answer is:

reckons

This clue is a double definition.

'calculates' is the first definition.
('reckon' can be a synonym of 'calculate')

'guesses' is the second definition.
(I know this)

'or' is the link.

(Other definitions for reckons that I've seen before include "Suspects" , "Considers" , "Judges" , "Conkers (anag.)" , "Counts or guesses" .)

I've seen this clue in The Everyman puzzle in The Observer.

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