Our reports are fully customised in CT but our calc times are being impacted by the calc on some OOTB reports. Is there a way of batch stopping these reports from calculating?

Great question Julie, one I do not know the answer to.  Let's check with @Chris Davidson, @Mark Nealey or @Stephen Atwell.  I'll also move this to another location to give it more visibility.  

When editing a report:

R11: (top) Ribbon > Author > Pre-load: Uncheck box.

R12: (top) Ribbon > Report > Active: Uncheck box.

Thank you Chris for always responding!  :-)  So we have to set this on each report individually?  I think Julie is wanting to do them in bulk - to all the out of the box at once.  Is that what you're asking Julie?

Just a comment: if you do this, your reports will not be available in Production.  This is to prevent performance issues that could occur if you tried to calculate an intensive report on the fly.

@Jenny Goodwin we're on Version r12.4.0486b13b4e4b.74069  & yes if we could do it in bulk that would be fantastic

@Diane Johnson this should be ok for us as we don't use any of the OOTB reports. 

oh, please confirm for me which version you're using?  (i think R12 but want to make sure before I move your question)