Exactly how you will validate this is really down to you: we have no idea how you are storing the info, or what needs verifying where, or even when.
But... working it out is pretty easy:
Assume you are working with today:
Dim today As DateTime = DateTime.Now.[Date]
Dim start As New DateTime(today.Year, today.Month, 1)
Dim [end] As DateTime = start.AddMonths(1).AddDays(-1)
Dim renew As DateTime = [end].AddYears(1)