Unfortunate consequences following American calculations? (9)
I believe the answer is:
aftermath
'unfortunate consequences' is the definition.
'following american calculations?' is the wordplay.
'following' becomes 'after' (I've seen this before).
'american calculations?' becomes 'math' (US term for maths).
'after'+'math'='AFTERMATH'
(Other definitions for aftermath that I've seen before include "Subsequent consequence" , "Subsequent circumstances" , "Frame that in following events" , "Consequences of a bad event" , "Wake" .)