hope i understand your question here.
use the same expression in Qlikview as well.
If you are doing this in the load script. it would look like,
LOAD
annual_leave - leaves_taken as carry_forward
From
Etc Etc..
IF you are doing at an expression level in a chart,
add the dimension you want to see the chart at
and in your expression you can just say Sum(annual_leave) - Sum(leaves_taken)
hope this helps.