increase date in derived field

i have two fields:

Issue date and Expiry date , the case is when  expiry date is empty it should be filled with value (Issue date plus five years)

i  use the following code in  Expiry date field is derived section, its working good but i cant add five years here:

<$if #active.xExpiry_Date like ""$>

<$dprDerivedValue=#active.xPOA_IssueDate$>

<$endif$>

 

then i use the following code , but i cant use (xPOA_IssueDate) field :

<$if #active.xExpiry_Date like ""$>

<$dprDerivedValue=dateCurrent(1811)$>

<$endif$>

any help please to use xPOA_IssueDate field and add to it five years?