An interest that will automatically come to an end on the occurrence of some specified event (which, however, may never happen). For example, if A conveys land to B until he marries, B has a determinable interest that would pass back to A upon his marriage. But if B dies a bachelor the possibility of a reverter to A is destroyed and B's heirs acquire an absolute interest. An interest that must end at some future point (e.g. a life interest) is not classified as a determinable interest, but one that could end during a person's life (for example a protective trust) is so classified. A determinable legal estate in land prior to 1925 was known as a determinable fee, but under the Law of Property Act 1925 it can now exist only as an equitable interest. It is exceptionally difficult to distinguish between a determinable interest and a conditional interest. Compare contingent interest.