10 percent for a straight layout in a simple rectangular room — the default. 15 percent the moment you have diagonal installation, multiple obstacles (columns, kitchen islands, odd corners), or rooms with lots of doorways and threshold transitions. 20 percent for herringbone, chevron, or other complex patterns that produce a lot of small unusable offcuts. Cheap laminate can afford generous wastage; expensive engineered wood or premium hardwood justifies more careful planning to keep the wastage closer to 10 percent because every wasted plank is real money.