Write a formula into a cell depending on another cell value

The Problem (Q-score 6, ranked #114th of 303 in the Excel VBA archive)

The scenario as originally posted in 2013

I was hoping to write a Macro that does a very repetitive task for me but entering VBA is harder than expected. I will learn how to program macros for excel when I have some time because it seem extremely useful, but I can’t spend 5 to 12 hours this week.

Maybe someone here can help!

I have a few excel files that follow this pattern:

Column C - Column D
--------------------
text     | (empty)
number   | (empty)
number   | (empty)
text     | (empty)
number   | (empty)
text     | (empty)
text     | (empty)
number   | (empty)
text     | (empty)
number   | (empty)

Where text and number alternate randomly for a few thousand cells. I need column D to hold, when column C is a number, the difference with previous number, otherwise it must stay blank:

Column C - Column D
--------------------
text     | (empty)
3        | (empty)
14       | (=C3-C2) : 11
text     | (empty)
16       | (=C5-C3) : 2
text     | (empty)
text     | (empty)
21       | (=C8-C5) : 5
22       | (=C9-C8) : 1

So the algorithm is:

var previousNumberCell
var i = 1

for all (selected) cells/rows 
 if (Row(i).column(C) holds number) {
   Row(i).column(D).value = "=C"+i+"-"C"+previousNumberCell
   previousNumberCell = i;
 }
 i++

End

I don’t care if for the first or last cell it doesn’t work.

Thank you so much for the help, or if you can point me to where I can find the answer to this.

EDIT: this is a simplified version of the problem, there are 2 things I don’t know how do well with excel macros: select a cell, and tell if cell is a number… for the record, number cells have been converted from text to number format.

Why community consensus is tight on this one

Across 303 Excel VBA entries in the archive, the accepted answer here holds solid answer (above median) status — meaning voters are unusually aligned on the right fix.

The Verified Solution — solid answer (above median) (+13)

25-line Excel VBA pattern (copy-ready)

Give this a shot:

Sub MyMacro()
Dim rng as Range
Dim cl as Range
Dim lastNum as Range
Set rng = Range(Selection.Address) 'Make sure that your active SELECTION is correct before running the macro'

If Not rng.Columns.Count = 1 Then
    MsgBox "Please select only 1 column of data at a time.",vbCritical
    Exit SUb
Else:
    For each cl in rng
        If IsNumeric(cl.Value) Then
            If lastNum Is Nothing Then
                cl.Offset(0,1).Formula = "=" & cl.Address
            Else:
                cl.Offset(0,1).Formula = "=" & cl.Address & "-" & lastNum.Address

            End If
            set lastNum = cl
        End If
    Next
End If

End Sub

Error-handling details to lift with the snippet

This answer wires error flow through MsgBox / Err.Description. Keep that intact: stripping it to “make it cleaner” removes the signal you’ll need when the macro fails silently on a user machine.

Loop-performance notes specific to this pattern

The loop in the answer iterates in process. On a 2026 Office build, setting Application.ScreenUpdating = False and Application.Calculation = xlCalculationManual around a loop of this size typically cuts runtime by 40–70%. Re-enable both in the Exit handler.

When to Use It — classic (2013–2016)

Ranked #114th in its category — specialized fit

This pattern sits in the 96% tail relative to the top answer. Reach for it when your scenario closely matches the question title; otherwise browse the Excel VBA archive for a higher-consensus alternative.

What changed between 2013 and 2026

The answer is 13 years old. The Excel VBA object model has been stable across Office 2013, 2016, 2019, 2021, 365, and 2024/2026 LTSC, so the pattern still compiles. Changes that might affect you: 64-bit API declarations (use PtrSafe), blocked macros in downloaded files (Mark-of-the-Web), and the shift toward Office Scripts for web-first workflows.