Apportion a value across cells with VBA

Today, I want to share a really useful time-saving macro with you.  It’s a macro to apportion a value across cells.  Now that I’ve written it, I’m starting to gain the benefits, and hopefully, you can too.

When to use the macro?

Let’s say you’ve got a list of individual items, which add up to $210.  Your boss wants to add an additional $21 for contingency.  How are you going to make the total equal $231?  There are a few options:

• Add an adjustment line with +$21
• Identify specific lines which can be increased to achieve the $231 total
• Spread the $21 increase equally across all the cells
• Apportion the $21 increase across each line item so that each item receives a fair proportion.

The VBA code below addresses the fourth option.  You could do this manually using formulas, which would be time-consuming.  Instead, the VBA method below takes just 2 seconds.

WARNING! – Macros cannot be undone.  Before using the code in this post, make sure it works the way you want.

The VBA code

Enter the following code into a standard module.

Sub ApportionValueAcrossCells()

Dim apportionValue As Double
Dim keepAsFormula As Long
Dim total As Double
Dim c As Range
Dim formulaString As String

'Get the existing total
total = Application.WorksheetFunction.Sum(Selection)

'Check that sum of selected cells is not zero
If total = 0 Then

    MsgBox Prompt:="Selected cells must not sum to zero", _
    Title:="Apportion value"
Exit Sub

End If

'Get the value to apportion
apportionValue = Application.InputBox(Prompt:="Value to apportion:", _
Title:="Apportion value", Type:=1)

'The User clicked Cancel
If apportionValue = False Then Exit Sub

'Get the boolean value to keep the formula or hardcode the result
keepAsFormula = MsgBox("Keep formula?", vbYesNo)

'Loop through each cell in selection
For Each c In Selection

    If IsNumeric(c.Value) Then

        'Calculate the result of the cell
        formulaString = c.Formula & "+(" & apportionValue & _
            "/" & total & "*" & c.Value & ")"

        If Left(formulaString, 1) <> "=" Then _
            formulaString = "=" & formulaString

        'Enter the formula into the cell
        c.Formula = formulaString

        'Recalculate the active cell
        ActiveCell.Calculate

        'If keepAsFormula is no, then hardcode the result
        If keepAsFormula = vbNo Then
            c.Value = c.Value
        End If

    End If

Next c

End Sub

How to use the code

To use the macro, follow these steps:

1. Select the cells which contain the current values
   
2. Run the macro
3. An Input Box will appear, enter the value you wish to adjust the total by, then click OK
   
4. A message box will appear.  The macro can either paste the new values or include the formula.  Click on the button with your preference.
   
5. Ta-dah! The values will be updated.  The 21 has now been apportioned across all the cells according to their original value.
   

Help me improve the macro

I’ve written this code to operate the way that I work and to meet my needs.  However, maybe you work differently, maybe you can think of some improvements, or maybe you have a different way to apportion a value across cells.  If so, please include your thoughts in the comments section below.

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