Bonjour,
Une autre proposition !
Sub Trouver_Date()
Dim dt, rngData As Range, lastCol As Long, n
With ActiveSheet
dt = .Cells(4, 1).Value2
lastCol = .Cells(1, .Columns.Count).End(xlToLeft).Column
Set rngData = .Cells(1).Resize(, lastCol)
n = Application.Match(dt, rngData, 0)
If IsError(n) Then
MsgBox "Date inconnue"
Else
.Cells(4, 3).Value = n
End If
End With
End Sub