There are long-standing bugs affecting the use of formfields for calculations using the results of other formfields. Why MS has never bothered to fix this is beyond me. That said, you can do all your calculations using formula fields. To see how to do a wide range of calculations in Word, check out my Microsoft Word Field Maths Tutorial, at:
http://windowssecrets.com/forums/sho...Maths-Tutorial
or:
http://www.gmayor.com/downloads.htm#Third_party

For Date/Time calculations, though, even using formula fields isn't straightforward. To see how to do this and just about everything else you might want to do with dates & times in Word, check out my Microsoft Word Date Calculation Tutorial, at:
http://windowssecrets.com/forums/sho...ation-Tutorial
or:
http://www.gmayor.com/downloads.htm#Third_party
Do read the document's introductory material.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]