NickyC thanks for coming up with that formula, I have a few questions about it...

firstly, would it be possible to explain each phrase in english so i can understand what its doing? (just to make sure its doing what i would like.... im not sure if i explained it properly)

secondly, you have A1 and B1 in that formula but dont state which ones they are? you could use this to explain:
start date = A1
end date = B1
as an example...

Also I notice you use round up and down. If possible, could the value be given as an exact number of hours (even if it goes into decimals) that way i could have a seperate column for rounding the values up or down if needs be...

lastly, will this make my excel slow down? im planning on autofilling a sheet with over 1000 rows with the formula once I can use it.

Thanks for your help, greatly appreciated.