You can't have your cake and eat it (too) is a popular English idiomatic proverb or figure of speech. The proverb literally means "you cannot simultaneously retain possession of a cake and eat it, too". Once the cake is eaten, it is gone. It can be used to say that one cannot have two incompatible things, or that one should not try to have more than is reasonable. The proverb's meaning is similar to the phrases "you can't have it both ways" and "you can't have the best of both worlds."

For those unfamiliar with it, the proverb may sound confusing due to the ambiguity of the word 'have', which can mean 'keep' or 'to have in one's possession', but which can also be used as a synonym for 'eat' (e.g. 'to have breakfast'). Some find the common form of the proverb to be incorrect or illogical and instead prefer: "You can't eat your cake and [then still] have it (too)". Indeed, this used to be the most common form of the expression until the 1930s–1940s, when it was overtaken by the have-eat variant. Another, less common, version uses 'keep' instead of 'have'.

Choosing between having and eating a cake illustrates the concept of trade-offs or opportunity cost.