When parties to a contract make promises to perform their obligations, and one party reasonably relies on the other party’s promise—but the party making the promise fails to perform, causing harm or loss to the party who relied on the promise—the party who relied on the promise to perform is said to have relied to its detriment.

This legal concept is called detrimental reliance. Detrimental reliance may serve as a substitute for consideration, and make an otherwise unenforceable contract enforceable.

Thus, detrimental reliance is a legal concept based on fairness (known as equity or equitable), and is equivalent to contractual promissory estoppel (due to the other party’s reliance, the party who did not keep its promise is prohibited from challenging the enforceability of its promise).

Detrimental reliance is not a separate tort cause of action.

In Montana, the legal concept of detrimental reliance, also known as promissory estoppel, is recognized and can be used to enforce a contract that may otherwise lack consideration and be unenforceable. Under Montana law, if a party makes a promise that leads another party to reasonably rely on that promise to their detriment, the promisor may be prevented from arguing that the promise is unenforceable. This doctrine is grounded in principles of fairness and aims to prevent injustice that would result from the promisor's failure to fulfill their promise. Detrimental reliance is not considered a separate tort but rather a principle that can create obligations similar to those in a contract based on the equities of the situation. An attorney can provide specific guidance on how this principle may apply in individual cases in Montana.