How to add two years to a metadata field date using idoc scripting

 In URM, I need to be able to derive a metadata field to equal the date of a different date field plus two years.

When I code this: 

<$dprDerivedValue=#active.xVIPContractExpDate$>

I end up getting the exact date that is in VIPContractExpDate derived into the metadata field.

So then I tried this:

<$dprDerivedValue=#active.xVIPContractExpDate(730)$>

thinking that this would add two years to the VIPContractExpDate, but it doesn't.  Instead it just leaves the field blank. 

Can anyone out there help me with the correct idoc code to be able to derive a metdata field to another one plus two years?