Under the common law, payment of a lesser sum of money than is owed in consideration of a promise to discharge a fully matured, undisputed debt is legally sufficient to support the promise of discharge.

Under common law, a promise to discharge a fully matured, undisputed debt for a lesser sum of money than is owed is not legally sufficient consideration to support the promise of discharge. This principle is known as the "pre-existing duty rule," which states that performing or promising to perform what one is already legally obligated to do does not constitute valid consideration for a new promise.