Excel - Currency changes format by itself

Excel randomly reverting currency format (especially negative numbers) is a known annoyance, particularly in Microsoft 365/Office 365 where auto-updates, region settings, or shared workbooks can quietly reset your formatting.

What you can maybe do…

Turn Off Auto Format from External Sources

File → Options → Advanced, Scroll to "Cut, copy, and paste"

Uncheck: “Show Paste Options button when content is pasted”

If It Still Reverts…

Check Windows Locale (Regional Settings):

Even if your Excel looks fine, Windows might be overriding it on file open.

Go to: Control Panel → Region → Formats → Additional Settings → Currency tab

Ensure:Currency symbol: $

Negative currency format: -$1,234.56 or your preferred style.

Try this format, maybe it helps…

"$"#,##0.00;[Red]"-$"#,##0.00

Or try to fix it with VBA

Private Sub Workbook_Open()
    Dim ws As Worksheet
    For Each ws In ThisWorkbook.Worksheets
        With ws.Range("B:B") ' change as needed
            .NumberFormat = "$#,##0.00;- $#,##0.00"
        End With
    Next ws
End Sub

Don’t forget to Save the file as .xlsm

My answers are voluntary and without guarantee!

Hope this will help you.