https://static.wixstatic.com/media/3d91ba_15dc7a50ccea4dc88856265fb0d8f969~mv2.gif
The recommended overlaps are:
• For horizontal, honeycomb, and pleated shades, add 1 1/2” to all sides (3” overall to width and height).
• For vertical blinds: Add 4” to each side and 2” to the top and bottom. If the blind reaches the floor or sill, only add 2” to the top