David wrote

=MAX(0,80-(SUM(N8:N12,N15:N19))-SUM(S8:V12,S15:V19))

Actually, I had to change the formula to:
=MAX(0,40-(SUM(N7:N13))-SUM(S7:V13))+MAX(0,40-(SUM(N14:N20))-SUM(S14:V20))
because used Annual Time is calculated in seperate weeks

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David