Hi Martin,
I came up with the following, but have just realised that your working week is 5 days. The following is based on 7, but you can no doubt modify it - I haven't time just at the moment.
I created a table of months with 1-12 in the first column and the days in each month in the second column, and named this table "ME_Table".
Then with the Monday week start days starting in A6 going down, e.g. 24/11, 1/12, 8/12 etc. and the days for that week in B6....the following formula in C6 apportions the days when a week straddles a month boundary.
=IF(OR(DAY(A7)=1,DAY(A6)=1),B6,IF(MONTH($A6)<>MONTH($A7),(VLOOKUP(MONTH(A6),me_table,2,FALSE)-DAY(A6)+1)/7*B6,IF(MONTH($A6)<>MONTH($A5),(DAY(A6)-1)/7*B5+B6,B6)))
As I say it perhaps wants tweaking to reflect 5 day working week. Then presumably you'll just have a second table of month names with a SUMIF() to add the week values in each month.
HTH
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