Lee Clark — Co-Founder & Business AttorneyDraws on 60+ years of combined firm experience guiding owners through contracts, deals, and disputes. About Lee →

Business relationships evolve, and the contracts governing them often need to change — a new deadline, an adjusted price, an expanded scope. But changing a contract informally, through a verbal agreement or just by acting differently, can create confusion about what actually governs and may result in unenforceable changes. Amending a contract correctly ensures the modification is clear and binding. This guide explains how to amend and modify existing contracts properly. It is general information, not advice on a specific contract.

We help businesses get this right from the start. This is general information, not advice on a specific situation.

A contract change made on a handshake is a dispute waiting to be had.

Why informal changes cause problems

When parties change how they operate under a contract without properly amending it — agreeing verbally, exchanging casual emails, or simply behaving differently — they create uncertainty about what actually governs the relationship. The original written contract says one thing; the parties are doing another. This gap breeds disputes about which terms apply, and informal changes may not be enforceable, especially where the contract requires modifications to be made a particular way. As the Legal Information Institute’s overview of a law.cornell.edu reflects, the terms that govern are those the parties have properly agreed. Informal modifications undermine that clarity, which is exactly why proper amendment matters.

How you change a contract determines whether the change actually counts.

Amend in writing, with mutual agreement

The reliable way to change a contract is a written amendment agreed to by both parties. A written amendment clearly states what’s being changed, leaves the rest of the contract intact, and is signed by the parties — creating an unambiguous record of the new terms. Mutual agreement is essential: one party generally can’t unilaterally change a contract; both must consent to the modification. Putting the change in writing, with both parties’ agreement, ensures the modification is clear and enforceable, rather than a contested verbal understanding. This is the foundation of amending a contract correctly — a documented, mutually-agreed, written change.

Follow the contract’s own rules

Many contracts specify how they may be modified — commonly requiring that changes be in writing and signed by both parties (a “no oral modification” clause). Where a contract contains such a provision, following it is important, because a change made contrary to the required method may be ineffective. So amending correctly means checking the contract’s own modification requirements and complying with them. This is a frequently overlooked step: parties agree to a change but don’t follow the procedure the contract itself demands, leaving the modification vulnerable. Respecting the contract’s rules for its own amendment is a key part of making changes that hold.

Getting amendments right

To amend a contract correctly: make the change in writing, ensure both parties agree and sign, clearly specify what’s being changed while confirming the rest of the contract remains in effect, and follow any modification procedure the contract requires. For significant changes, having the amendment drafted or reviewed helps ensure it accomplishes what you intend without creating new ambiguities or conflicts with the existing terms. Because informal changes create confusion and may be unenforceable, and because a poorly drafted amendment can itself cause problems, handling contract modifications properly — with legal guidance for important ones — ensures the changes are clear, agreed, and enforceable. Proper amendment protects the relationship as it evolves.

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