To answer your particular question using your existing formula please try this:
-Add these two functions to a standard module
Code:
Public Function Min2(a As Variant, b As Variant) As Variant
'
' Returns the lesser of 2 values
'
Min2 = IIf(a < b, a, b)
End Function
Public Function Max2(a As Variant, b As Variant) As Variant
'
' Returns the greater of 2 values
'
Max2 = IIf(a > b, a, b)
End Function
Modify your formula:
Service to date - =Int(DateDiff("yyyy",[Reg],[Left])+DateDiff("yyyy",[Returned],[Left2])+DateDiff("yyyy",[Returned2],Min2(Date(),[Retired]))/365.25)
Again, I would follow the suggestions offered here, but I think this would address your current question.
Cheers,
Vlad