Does a pre-existing duty rule apply when one party promises something that they already owe to the other party?

However, where one party promises something in exchange that they already owe to the other party, they have, in effect, given nothing in exchange, and courts have held that this does not amount to consideration. This so‑called pre‑existing duty rule is usually traced back to the decision in Stilk v. Myrick, [1809] EWHC KB J58, (1809) 170 E.R. 1168.

In Stilk v. Myrick, two members of a sailing crew had deserted and the defendant captain promised the remaining crew members, of which the plaintiff was one, that he would increase their wages upon their return to London. The contract to pay additional wages was unenforceable for lack of consideration as the plaintiff crew member had already been under an obligation to do his utmost to allow the ship to reach her destination, including in the case of emergencies such as when crew members die or desert.