If I understand your question correctly that's easy. You could pass the function how the date should be calculated as a delegate to the constructor of your class. Example:
Public Class Program
Public Shared Sub Main()
Dim ex1 As New Example(Function(v) DateTime.Now.AddDays(v))
Dim ex2 As New Example(Function(v) DateTime.Now.AddYears(v))
Console.WriteLine(ex1.CalculateDate(1))
Console.WriteLine(ex1.CalculateDate(2))
Console.WriteLine(ex2.CalculateDate(1))
Console.WriteLine(ex2.CalculateDate(2))
End Sub
End Class
Public Class Example
Private ReadOnly DateCalculation As Func(Of Short, DateTime)
Public Sub New(dateCalculation1 As Func(Of Short, DateTime))
DateCalculation = dateCalculation1
End Sub
Public Function CalculateDate(val As Short) As DateTime
Return DateCalculation(val)
End Function
End Class
Console output:
5/13/2015 3:49:14 PM
5/14/2015 3:49:14 PM
5/12/2016 3:49:14 PM
5/12/2017 3:49:14 PM