Unilateral Contracts: What Are They? (2026 Updated)

You’ve probably agreed to a unilateral contract without even realising it.

Think about a public reward offer (“$500 for the return of my lost laptop”), a customer promotion (“free coffee if you show this voucher”), or a platform offer (“we’ll pay you if you complete X tasks”). In each case, one party makes a promise to the world (or to a group), and the other party accepts by doing something.

That’s the key feature of a unilateral contract: acceptance happens through performance, not by signing and returning an agreement.

This guide is updated for 2026 so it reflects how unilateral contracts commonly show up in modern business-especially in online advertising, promotions, marketplaces and service-based work-while keeping the legal principles clear and practical.

Let’s break down what unilateral contracts are in New Zealand, when they become legally binding, what can go wrong, and how to set your business up to be protected from day one.

What Is A Unilateral Contract?

A unilateral contract is a type of contract where:

• One party makes a promise (the “offer”) to another party or to the public, and
• The other party accepts the offer by performing an act (not by promising to perform).

This is different to a “typical” contract you might picture (like a signed service agreement), which is usually a bilateral contract-where both sides exchange promises (for example, “I’ll provide services” and “you’ll pay me”).

With unilateral contracts, there’s often no negotiation and no signature. The offeror controls the terms, and the offeree chooses whether to accept by completing the required action.

Common Examples Of Unilateral Contracts In NZ Business

Unilateral contracts come up more often than you’d expect, especially for small businesses running promos or public-facing offers. Examples include:

• Rewards: “$1,000 reward for information leading to the return of our stolen trailer.”
• Promotions: “First 50 customers get a free gift if you spend over $100.”
• Competitions and giveaways: “Enter by tagging a friend and following our page.”
• Referral incentives: “We’ll pay you $200 if you refer a client who signs up.”
• Public guarantees: “If you don’t see results in 30 days, we’ll refund you.”
• Some platform/task offers: “Complete the onboarding checklist and get a bonus.”

Because unilateral contracts can be created through marketing and day-to-day communications, they’re an area where businesses can accidentally make enforceable promises-without intending to.

How Does A Unilateral Contract Become Legally Binding?

In New Zealand, a unilateral contract generally becomes binding when the offeree performs the act required by the offer-as long as the usual elements of a contract are present.

Even though unilateral contracts can look informal, the law still asks the same core questions. In plain terms, you’re looking at:

• Offer: Was there a clear promise on specific terms?
• Acceptance: Did the other party accept by doing the required act?
• Consideration: Was something of value exchanged (often the act itself)?
• Intention: Did the parties objectively intend to create legal relations?
• Certainty: Were the terms clear enough to enforce?

If these elements line up, a unilateral contract can be enforceable even if:

• nothing is signed
• the offer was published on social media
• the “contract” is effectively a public promise

Offer Vs “Invitation To Treat” (Why Wording Matters)

One common grey area is whether what you said was a true offer, or just an “invitation to treat” (an invitation for someone to make an offer to you).

For example:

• “Reward: $500 for the return of X item” looks like a clear offer.
• “Contact us if you have information about X” may be more like an invitation to discuss.

If you want a message to be marketing rather than a legally binding promise, your wording (and any conditions) matter a lot.

Can You Revoke A Unilateral Offer?

Sometimes, yes-but it depends on timing and how the offer was communicated.

As a practical rule, once someone has started performing in reliance on your offer, trying to withdraw the offer can create serious risk. Even if you think you’re free to change your mind, the other party may argue they acted based on your promise and you should be held to it.

This is why “we can cancel anytime” type disclaimers can be helpful, but they’re not a magic shield-especially if your overall messaging is misleading or inconsistent.

Unilateral Contracts In Advertising, Rewards, And Promotions

For many small businesses, the biggest risk with unilateral contracts isn’t a formal legal dispute-it’s the day-to-day fallout when customers or members of the public expect you to honour a promise you made publicly.

That risk is both:

• contractual (someone might claim you entered into a binding agreement), and
• regulatory (your advertising or promo could breach consumer law if it’s misleading).

Fair Trading Act 1986: Don’t Make Promises You Can’t Back Up

If your unilateral “offer” is made in trade (for example, as part of promoting your business), you also need to think about the Fair Trading Act 1986. In simple terms, this Act prohibits misleading or deceptive conduct and false or misleading representations.

So if you run a promotion like “guaranteed results” or “free gift for every order,” you should be confident you can deliver exactly what you’ve promised-or make sure the conditions are clear and prominently stated.

It’s also where businesses get caught out by vague advertising like:

• “Free delivery” (but only in certain areas)
• “Limited time only” (but it runs for months)
• “First 100 customers” (but you don’t track it properly)

Even if you didn’t intend to create a contract, your marketing can still create legal obligations or enforcement risk if it misleads people.

Competitions, Giveaways And Promo Terms

If you’re running promotions, it’s smart to have clear rules (who can enter, how winners are chosen, timing, exclusions, what happens if the prize is unavailable). This reduces disputes and helps show what you meant by the “offer.”

For many businesses, having Competition Terms & Conditions in place is the simplest way to avoid confusion-especially when social media posts have limited space and people only read the headline promise.

Refund Promises And “Guarantees”

Another common unilateral-contract-style promise is a guarantee: “If you’re not satisfied, we’ll refund you.”

That can be a great sales tool-but it needs to be consistent with how you actually handle refunds, exchanges, and complaints. If you’re offering services (or selling products), a clear refunds approach can help you stay compliant and reduce misunderstandings.

Many businesses set this out alongside their customer-facing terms, for example in their Returns, Refunds And Exchanges approach and broader terms of sale.

What Are The Risks Of Unilateral Contracts For Business Owners?

Unilateral contracts can be useful (they help you market confidently and incentivise behaviour), but they also come with some very real business risks-particularly when offers are made quickly, informally, or across multiple platforms.

1. Accidental Legal Obligations

If you say “we will do X if you do Y,” and someone does Y, you may have created an enforceable obligation to do X-even if you didn’t mean it that way.

This often happens with:

• staff making informal promises to customers
• marketing posts written quickly without approvals
• offers made in DMs, emails, or quotes that weren’t reviewed

If you use quotes regularly, it’s also worth understanding when a quote becomes binding and what language should sit around it, because it can overlap with unilateral/bilateral concepts depending on how it’s framed. (This comes up a lot in service businesses.)

2. Disputes About Whether Someone Completed The “Act”

Because acceptance is by performance, disputes often become factual:

• Did the person actually meet the conditions?
• Did they perform within time?
• Was the act done properly (or just partially)?
• How do you verify performance?

If you don’t define the conditions clearly, you’re leaving a gap that can turn into an argument-especially if money, discounts, or reputational issues are involved.

3. Confusion Inside Your Own Business

Even if your offer is legally sound, problems arise when your team isn’t aligned on what the promise means.

For example:

• One staff member thinks the promo applies to all products; another thinks it’s only certain lines.
• Your website says one thing, your Instagram post says another, and your in-store signage says something else.
• Your customer support team doesn’t have the authority to honour the “offer,” leading to delays and complaints.

Strong internal processes help, but the best starting point is to make sure your “offer” is properly drafted and consistent with your broader customer terms.

4. Reputational Fallout (Even Without A Lawsuit)

Most unilateral contract issues don’t end up in court. They end up in:

• negative Google reviews
• social media backlash
• refund demands and escalated complaints

Getting the legal foundations right early isn’t just about avoiding disputes-it’s about keeping customer trust and protecting your brand as you grow.

How Can You Use Unilateral Contracts Safely In Your Business?

You don’t need to avoid unilateral contracts entirely. The goal is to use them intentionally, with clear wording and the right supporting documents-so you’re protected from day one.

1. Make The Conditions Clear (And Easy To Find)

If your offer depends on conditions, write them in plain English and make them accessible. Common terms to clarify include:

• Eligibility: Who can participate? (NZ only? Over 18? Existing customers excluded?)
• Time limits: Start/end dates and times (including time zone).
• How to claim: What proof is needed? Who do they contact?
• Limits: One per customer? While stocks last? Maximum number of redemptions?
• Exclusions: Certain products/services excluded?
• Substitution rights: Can you replace a prize/item if unavailable?

If you’re publishing offers online, it’s also wise to ensure your website terms align with your promos, for example your Website Terms & Conditions and (where relevant) e-commerce terms.

2. Avoid “Absolute” Language Unless You Mean It

Words like “guaranteed,” “always,” “no matter what,” and “unlimited” can create expectations that are hard to deliver-and hard to defend if challenged.

A safer approach is to be specific. For example:

• Instead of “free returns,” consider “returns accepted within 14 days for unused items (exclusions apply).”
• Instead of “refund if not satisfied,” specify the process and what “not satisfied” means.

You can still write in a customer-friendly way without leaving your business exposed.

3. Think About How You’ll Prove Performance

Because acceptance is by performance, you should think ahead: what evidence will show the conditions were met?

This might include:

• purchase receipts or order numbers
• time-stamped entries
• referral tracking links
• confirmation emails

When you’ve got a system in place, it’s easier to resolve disputes quickly and fairly.

4. Line Up Your Contracts With Your Offer (So Everything Works Together)

Unilateral offers often sit on top of (or alongside) your broader business arrangements. For example:

• If you’re offering a “bonus” for a referral, you might also need a proper Referral Agreement (especially if the referral relationship is ongoing or involves commissions).
• If you’re supplying services, your offer should be consistent with your core Service Agreement so you don’t accidentally contradict your payment terms, scope, or limitation of liability.
• If you’re using contractors or brand ambassadors to promote offers, make sure their arrangement is documented and clear, such as with a Influencer Agreement where relevant.

This “documents working together” approach is a big part of building strong legal foundations-because the risk usually isn’t one single promise, it’s inconsistency across multiple documents and channels.

5. Keep Privacy In Mind If The Offer Collects Personal Information

Many unilateral offers involve collecting personal information-think competition entries, email sign-ups, loyalty programs, referral forms, or “claim your reward” pages.

If you’re collecting names, emails, phone numbers, addresses, or any other identifiable data, you should make sure you comply with the Privacy Act 2020 and clearly communicate what you’re doing with that data.

In practice, that usually means having a clear Privacy Policy and (depending on the context) a collection notice at the point you collect the information.

Key Takeaways

• A unilateral contract is where one party makes an offer and the other party accepts by performing an act (not by making a promise).
• Unilateral contracts can be legally binding in New Zealand even without a signature, especially in rewards, promotions, and public offers.
• To be enforceable, the arrangement still needs the core contract elements like offer, acceptance by performance, consideration, intention, and certainty.
• Marketing language matters-unclear or overly broad promotions can create accidental obligations and may also raise issues under the Fair Trading Act 1986.
• Clear promo rules, well-drafted terms, and consistent business documents (like Website Terms & Conditions and a Service Agreement) reduce disputes and protect your business from day one.
• If your offer collects customer data (like competition entries or referral sign-ups), make sure your Privacy Act 2020 compliance is covered with a clear Privacy Policy and collection practices.

If you’d like help setting up clear terms for promotions, rewards, referral arrangements, or customer offers (so you don’t accidentally create obligations you can’t manage), you can reach us at 0800 002 184 or team@sprintlaw.co.nz for a free, no-obligations chat.