恒常所得假说（英语：Permanent income Hypothesis，缩写为 PIH），由美国经济学家米尔顿·傅利曼所发展出的消费理论，在1957年提出。所谓的恒常所得（permanent income）是指长期的预期平均收入。简单来说，这个假说认为，消费者做出的选择，它所形成的消费模式，是由消费者的永久收入（permanent income）的改变来决定，而不是暂时收入的改变。这个理论的主要结论是，暂时性的收入改变，对消费支出行为只会有很小的影响，但是永久收入的改变，对消费支出行为则会有很大的影响。

The permanent income hypothesis (PIH) is an economic theory attempting to describe how agents spread consumption over their lifetimes. First developed by Milton Friedman, it supposes that a person's consumption at a point in time is determined not just by their current income but also by their expected income in future years—their "permanent income". In its simplest form, the hypothesis states that changes in permanent income, rather than changes in temporary income, are what drive the changes in a consumer's consumption patterns. Its predictions of consumption smoothing, where people spread out transitory changes in income over time, departs from the traditional Keynesian emphasis on the marginal propensity to consume. It has had a profound effect on the study of consumer behavior, and provides an explanation for some of the failures of Keynesian demand management techniques.