Thanks for your help macropod. Although I am now struggling to input the DateDiff function into the document! Just to clarify, I don't need it as a Message Box, but for it to become text to input into the documnet itself.

I have tried to do this by

Dim TheDate As Date
Dim AgeofPlan As Date
TheDate = DTPStartDate.Value
AgeofPlan = DateDiff(yyyy, TheDate, Now)

But keep getting a Run-time error '5': Invalid procedure call or argument on the last line.