SQL Semi annual due date

Hello,  I need to calculate a semi annual date due date based on an issue date. 

I have a case statement for Annual and Quarterly but wondering if there is a statement that would calcualte semi annual?

case when ps.PaymentMode = 'Annual' then
   case when (DATEADD(year, datediff(year, ps.[IssueDate], getdate()), ps.IssueDate ) > getdate() )
   then dateadd(year, datediff(year, ps.issuedate, getdate()), ps.issuedate)
   else dateadd(year, datediff(year, ps.issuedate, getdate())+1, ps.issuedate) end
 
   Else
  case when ps.paymentmode = 'Quarterly' then
   case when (dateadd(quarter, datediff(quarter, ps.issuedate, getdate()), ps.issuedate) > getdate() )
   then dateadd(quarter, datediff(quarter, ps.issuedate, getdate()), ps.issuedate)
  else dateadd(quarter, datediff(quarter, ps.issuedate, getdate())+1, ps.issuedate)  end

   end
   end as 'Premium Due Date'

Thanks!