Whenever I’m offered an extended warranty, I ask myself what the probability is that the item will break after the manufacturer’s warranty expires and before the extended warranty does. Then, I multiply that by the cost of the item. If the extended warranty costs less than that (it rarely does), I buy it. Otherwise I politely decline it.

Usually, items that break do so either very early (“infant mortality,” sorry, they really do call it that), or after many years, usually after the extended warranty runs out…