Bonsoir,
A tester :
Sub Interpoler()
Dim T(), e#, n&, i&, d%
With ActiveSheet
n = .Cells(.Rows.Count, 1).End(xlUp).Row
ReDim T(5 To n, 1 To 1)
For i = 5 To n Step 5
T(i, 1) = .Cells(i, 2)
If .Cells(i, 2) <> "" And .Cells(i + 5, 2) <> "" Then
e = (.Cells(i + 5, 2) - T(i, 1)) / 5
For d = 1 To 4
T(i + d, 1) = T(i, 1) + e * d
Next d
End If
Next i
.Cells(5, 2).Resize(n - 4).Value = T
End With
End Sub
Cordialement.