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 Colorado, 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. This principle is grounded in equity, aiming to prevent injustice by holding a party accountable when another party has reasonably relied on their promise to their detriment. For promissory estoppel to apply, the party claiming it must typically show that a promise was made, they relied on that promise reasonably and to their detriment, and that it would be unjust not to enforce the promise. While detrimental reliance is related to contract law, it is not considered a separate tort cause of action. Instead, it is a doctrine that can create obligations similar to those in a contract, to prevent a party from arguing that their unfulfilled promise should not be enforced.