According to Consumer Reports, December is the best month for purchasing large appliances, which includes dishwashers. HouseLogic.com recommends looking for deals in September, October and January.
New appliance models are typically unveiled in the fall, which means that retailers often offer sales to clear floor and inventory space. Most sales for large appliances are for previous year models; new models are typically not discounted.
How often appliances go on sale can vary based on how the store operates. Large stores with extra space to handle for new appliances may only offer sales if they've struggled to sell other types of products, while small stores might offer more predictable sales.