Legal Definitions - Pre-existing duty doctrine

The Pre-existing duty doctrine is a principle in contract law designed to prevent one party from unfairly demanding more payment or a new benefit for simply doing what they are already legally obligated to do under an existing contract. In simpler terms, if you've already promised to perform a specific task or service, you can't later ask for extra compensation or a new advantage just for completing that same original promise, unless the other party receives something new of value in return.

For a contract modification to be legally binding, both parties must exchange something new of value, known as "consideration." If a modification only requires one party to perform a duty they already owed, without receiving anything new in return, then there's no new consideration for that modification, and it might not be enforceable.

Here are some examples to illustrate this doctrine:

• Construction Project: Imagine a homeowner hires a contractor to build a new patio for a fixed price of $8,000. The contract specifies all materials and labor. Halfway through the project, the contractor stops work and tells the homeowner they will only finish if the homeowner agrees to pay an additional $1,500, claiming the work is "more difficult than expected."

  How it applies: The contractor has a pre-existing duty to complete the patio for $8,000 as per the original agreement. Demanding an extra $1,500 without offering any additional work, higher-quality materials, or other new benefits means there is no new "consideration" for this increased payment. Under the pre-existing duty doctrine, the homeowner could refuse to pay the additional $1,500, and the contractor would still be legally obligated to finish the patio for the original $8,000.

• Software Development Agreement: A small business contracts with a software developer to create a custom mobile application for a set fee of $15,000. The agreement outlines all the features and functionalities to be included. After the project is 80% complete, the developer informs the business that they will only deliver the final, fully functional app if the business agrees to pay an extra $3,000, citing "unexpected challenges in coding."

  How it applies: The software developer has a pre-existing duty to deliver the specified mobile application for $15,000. Their demand for an additional $3,000 to complete the *same* work, without adding new features or providing any other new value to the business, lacks new consideration. The business could argue that this modification is unenforceable because the developer is merely asking for more money to fulfill an existing contractual obligation.

• Catering Service: A client hires a catering company to provide food and service for a corporate event, agreeing to a menu and a total price of $2,500. Two days before the event, the catering company calls the client and states they will only provide the dessert course if the client pays an additional $200, claiming a sudden increase in ingredient costs.

  How it applies: The catering company has a pre-existing duty to provide the entire agreed-upon menu, including the dessert course, for the original $2,500. Asking for an extra $200 for a component already covered by their existing contract, without offering a new or upgraded dessert, means there is no new consideration for this additional payment. The client could refuse to pay the extra $200, as the catering company is simply performing a duty they already promised.