Calculate number of days excluding holidays and weekends

Hi,

I have two dates - order start date & shipment date.

I want to work out the number of days i have these products in house. however, i want to exclude weekends, holidays and time on hold. I have the date on hold in a column.

Can anyone advise a formula that I can use for this, I want the answer to return the number of days I've had it in house, example below.

order start on hold ship date

Mon 01/04/12 Wed 03/04/12 05/04/12


Time in house = (ship date - order start) - on hold
4 days = (05/04/12 - 01/04/12) - 03/04/12

Thanks

David