Hello Martyn,

I'm not sure I agree with all your results - how is E7 = 21 or D10 = 48?

Try this formula in D6 copied down

=IF(B6="","",MAX(0,NETWORKDAYS(B6,IF(C6="",B$3,C6))))

and this one in E6

=IF(B6="","",MAX(0,NETWORKDAYS(MAX(B6,B$2),MIN(IF(C6="",B$3,C6),B$3))))