To format a negative percentage to appear in parentheses instead of with a minus sign in Excel:

1. Select the cell or range of cells that you want to format.
2. Right-click on the selection and choose "Format Cells" from the context menu.
3. In the Format Cells dialog box, select the "Custom" category.
4. In the "Type" field, enter the following custom number format:
   Formula:

   0.0%;(0.0%) 

5. Click "OK" to apply the format to the selected cells.

This custom number format will display positive percentages as usual (e.g. 5.2%), but negative percentages will be enclosed in parentheses (e.g. (5.2%)). You can use these formatted values in formulas just like any other numeric value.