=SOMMEPROD((MOIS(LIGNE(INDIRECT(A1&":"&B1)))=2)*(JOUR(LIGNE(INDIRECT(A1&":"&B1)))=29))
Function NbAnBissex(DateDeb As Date, DateFin As Date) As Long
Dim AnDeb As Long, AnFin As Long, i As Long
NbAnBissex = 0
AnDeb = Year(DateDeb)
AnFin = Year(DateFin)
If Month(DateDeb) > 2 Then AnDeb = AnDeb + 1
If DateFin <= DateSerial(AnFin, 2, 28) Then AnFin = AnFin - 1
For i = AnDeb To AnFin
If Month(DateSerial(i, 2, 29)) = 2 Then NbAnBissex = NbAnBissex + 1
Next i
End Function
Msgbox nb_bissex(Range("A1").value, Range("B1").value)
Msgbox an_bissex(Range("A1").value, Range("B1").value)
Msgbox NbAnBissex(Range("A1").value, Range("B1").value)