Automatically Update Date in Cell if Another Cell is Modified

As an example:

Let's say you want to update the date in T2:T100 if any cell in the same row in columns A to M is changed.

Right-click the sheet tab.

Select 'View Code' from the context menu.

Copy the code listed below into the worksheet module.

Switch back to Excel.

Save the workbook as a macro-enabled workbook (*.xlsm).

Make sure that you allow macros when you open the workbook.

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim rng As Range
    If Not Intersect(Range("A2:M100"), Target) Is Nothing Then
        Application.ScreenUpdating = False
        Application.EnableEvents = False
        For Each rng In Intersect(Range("A2:M100"), Target).Rows
            Range("T" & rng.Row).Value = Date ' or Now if you want date+time
        Next rng
        Application.EnableEvents = True
        Application.ScreenUpdating = True
    End If
End Sub