Forcing a Macro to Run When a Worksheet is Recalculated

When you write a macro, it is designed to be run whenever you choose to run it. What if you need to develop a macro that will run whenever something changes in your worksheet? What if you want the macro to run automatically? This is particularly necessary if you are creating a custom function that you want to use within the cells of the worksheet.

This is where the Volatile method comes in handy. All you need to do is include the following statement within your macro:

Application.Volatile

This informs Excel that the results of the macro are dependent on the values in the worksheet, and that it should be executed whenever the worksheet is recalculated. For instance, consider the following user-defined function:

Function CountCells(MyRange As Range)
    Dim iCount As Integer
    iCount = 0
    For Each cell In MyRange
        If cell.HasFormula Then
            iCount = iCount + 1
        End If
    Next cell
    CountCells = iCount
End Function

This function, if used in a cell, counts the number of cells that contain formulas within a specified range. However, the function will only run the first time it is entered into a cell, or whenever the cell containing the formula is edited. If you want the function to recalculate every time the worksheet is recalculated, you would add the Volatile method near the beginning of the function:

Function CountCells(MyRange As Range)
    Dim iCount As Integer
    Application.Volatile
    iCount = 0
    For Each cell In MyRange
        If cell.HasFormula Then
            iCount = iCount + 1
        End If
    Next cell
    CountCells = iCount
End Function

The inclusion of the Application.Volatile method means that every time the worksheet is recalculated, this function (macro) is again run.