Conocer si es año bisiesto.

Function BisiestoSINO(Year As Date) As Boolean
    Dim Mod400 As Long, Mod100 As Long, Mod4 As Long
    
    BisiestoSINO = False 'Indica si es bisiesto o no
    Mod400 = Year Mod 400
    Mod100 = Year Mod 100
    Mod4 = Year Mod 4
    
    If (Mod400 = 0) Then BisiestoSINO = True
    If (Mod100 = 0) And (Mod400 <> 0) Then BisiestoSINO = False
    If (Mod4 = 0) And (Mod100 <> 0) Or ((Mod4 = 0) And (Mod400 = 0)) Then BisiestoSINO = True
End Function

Function BisiestoSINO(Year As Date) As Boolean
    BisiestoSINO = Day(DateSerial(Year(Fecha), 3, 0)) = 29
End Function