mainly British old-fashioned to calculate the total amount of something
I'll just reckon up how much you owe me.
phrasereckon up reckon up sth • reckon sth upBrE old-fashioned to add up several amounts in order to get a total: $17.60 plus tax is $20.68, if I've reckoned it up correctly.Pat nodded her head, reckoning up the cost of everything in her mind.■ SIMILAR TO: add up