Flag value in col d based on value in col b

Hi, welcome to the forum

Have you looked at using Conditional Formatting for this?
1. highlight the range you want to apply the conditional formatting to (the range in column D)
2. on the home tab, styles, select CF
3. select new rule, select use formula
4. enter =A2<30 format as required

Hi SGW, maybe this?

Sub checkb()

Dim ws As Worksheet 'to set worksheet
Dim lr As Long 'to find last used row in column B (assuming you want to check only cells with data
Dim i As Long

Set ws = Worksheets("Sheet1") 'change Sheet1 to the name of the sheet you are checking.
lr = ws.Range("B" & Rows.Count).End(xlUp).Row
For i = 1 To lr 'change 1 to the first row of data you wish to check
    If ws.Range("B" & i).Value < 30 Then ws.Range("D" & i).NumberFormat = "$#,##0.00"
Next i

End Sub

sgw your code would check every used cell on the active sheet, did you look at the code I posted?

SGW across ALL sheets?

You can replace the "set ws = " line with set ws = activesheet, so you can activate the sheet you want, call macro, and activate next sheet, etc

Sub checkb()

Dim ws As Worksheet 'to set worksheet
Dim lr As Long 'to find last used row in column B (assuming you want to check only cells with data
Dim i As Long

For Each ws In ActiveWorkbook.Worksheets
    ws.Activate
    MsgBox ws.Name
    lr = ws.Range("B" & Rows.Count).End(xlUp).Row
    For i = 1 To lr 'change 1 to the first row of data you wish to check
        If ws.Range("B" & i).Value < 30 Then ws.Range("D" & i).NumberFormat = "$#,##0.00"
    Next i
Next ws

End Sub

Works on my end, but it only works through rows where b is not blank.
Let me know if and when I can help more