Sorry but that terminology is unfamiliar to me.  Can you give an example?
Possibly even upload an image of what you currently have. (Upload Images in your original post)

Ah that makes sense now.  I was thinking employment.

You might check out this video:  Manage Rental Inventory

Hopefully the check out date and check in date is what you are looking for.

Thank you, I'll watch it now.

Unfortunately, that video didn't give me my answer. Or I didn't see the formulas needed lol Any other suggestions?

Are you trying to workout how long a piece of equipment is hired out?
If this is the case you'll need DateDiff or you can use simple Date Math.

the WOH on hire box is working out how long it's been on hire for - I need it to stop counting however once the off-hire date box has been populated. Is that possible?
Thanks

Can't you just check if the box has a value or not.

If Not IsNull(OffHireDate) then
    'Do some stuff
End If

If you are using a Timer event to count up the days you could set the Timer Interval to 0 when the field is updated.
Without knowing how your counter works it may be hard for us to give a definitive answer.

Picture uploaded of how I get my current WOH to work.
Once I add a date to the Off-hire date, how can I get the WOH to calculate from the Order date to the off-hire date instead?
thanks

Try this.

DateCount: IIF(IsNull([OffHireDate]), Date()-[OrderDate], [OffHireDate]-[OrderDate])

awesome!! thanks Kevin...