MS excel to increase selected field value by N %

Actually, the formula above will DECREASE the value in the cell...

A1 * 30 / 100 = A1 * 0.3

You need to multiply by ( 1 + n%)

You can do this either by formula, with the result ending up in a different cell, or you apply this to all selected cells and the result will be in the same cells as the original value... using COPY / PASTE SPECIAL / MULTIPLY

To do this, enter the factor that you want to apply (say 1.3) in a cell. Select that cell and copy it.

Select the range of cells you want to change, click the Paste drop down arrow, select "Paste Special", then select the "Multiply" radio button, and [OK].



Note: If your cells that you are changing have a formula, then the formula is adjusted to include the "*1.3" or whatever you're multiplying by.


Doing this with a macro / vba would be something like:

Option Explicit

Sub MultiplyByFactor()

Dim rngFactor As Range
Dim rng As Range

    Set rngFactor = Application.InputBox("Pick the cell with the factor:", "Select one cell", Type:=8)
    Do While rngFactor.Cells.Count > 1
        If MsgBox("Please select ONE cell only", vbOKCancel, "Uno") = vbCancel Then
            Exit Sub
        End If
        Set rngFactor = Application.InputBox("Pick the cell with the factor:", "Select one cell", Type:=8)
    Loop

    Set rng = Application.InputBox("Pick range to apply this factor to:", "Select one or more cells", Type:=8)
    
    rngFactor.Copy
    rng.PasteSpecial Paste:=xlPasteAll, Operation:=xlMultiply, SkipBlanks:=False, Transpose:=False
End Sub

Quote:

How do I increase value of selected field by N%

1 prepare a cell with the value you need. Adding N% is multiplying.
-Source cell is =1+N/100
2 Copy that cell
3 Use paste-special with multiplication on target cells.

Have a look here:
Use Paste Special to perform calculations while pasting in Excel - TechRepublic[^]