Excel 2007 : excel formula for skipping holidays

[gladders]

Hi all,

I've been given a tricky task at work I'm having terrible trouble figuring out. Basically I have to figure out due dates, but exclude recess dates and holidays.

So I have dates in column A, and column B lists the date 21 days on (so for example A1+21). And column C has the date 39 days on from the days in column A.

What I can't figure out is how to instruct Excel to include weekends but exclude holidays from counting in columns B and C.

I've seen some formulae on other websites but there's been no explanation of what the components do, so when I've tried to tailor it to my spreadsheet I haven't a clue what I'm doing!

If anyone can explain this below, which has been described to me as the formula to use:

=IF(G3="","",G3+MAX(IF(ISNA(MATCH(G3+ROW(A$1:INDEX(A:A,21)),$H$1:$H$10,0)),ROW(A$1:INDEX(A:A,21)))))

Any help people could provide would be most appreciated