Unilateral Vs Bilateral Contracts: Key Differences In Agreements

If you run a small business, you’re signing (or relying on) contracts all the time - even when it doesn’t feel like it. Quotes, purchase orders, refund offers, loyalty promos, supplier onboarding, website terms, and service bookings can all create legal obligations.

One of the simplest (and most useful) ways to understand what you’re agreeing to is to know whether you’re dealing with a unilateral or a bilateral contract. Getting this wrong can lead to awkward disputes like: “But we never agreed to that” versus “You accepted the offer by doing the thing.”

In this guide, we’ll break down unilateral vs bilateral contracts in New Zealand in plain English, with examples that match how business actually works - plus the practical steps you can take to reduce risk and make your agreements enforceable.

What Is A Unilateral Contract In New Zealand?

A unilateral contract is a contract where one party makes a promise, and the other party accepts by performing an act (rather than promising to do something).

In other words, it’s a “do X and you’ll get Y” type of arrangement.

How Acceptance Works In A Unilateral Contract

In unilateral contracts, acceptance happens through performance. That’s why these agreements often show up in real-world business situations like promotions, rewards, incentives, and public offers.

Common features include:

• One clear offer made to a person or group (sometimes the public at large).
• No obligation on the other party to perform - but if they do perform, you may be bound to deliver what you promised (assuming the terms are clear and lawful).
• Acceptance is not a signature; it’s completing the required act.

As a practical point, timing can matter: many unilateral offers are treated as accepted when the required act is completed, and in some situations you may not be able to withdraw the offer once someone has started performing in reliance on it. This is one reason why clear conditions, cut-offs and eligibility rules are so important.

Everyday Business Examples Of Unilateral Contracts

Unilateral contracts are common in marketing and operational promises, for example:

• Promotions: “Bring in this flyer and get 20% off your next service.”
• Bounties or rewards: “We’ll pay $500 to anyone who finds and reports a critical security bug.”
• Return incentives: “Leave a review and receive a free add-on item.” (This can raise advertising and fairness issues if not done properly.)
• Public offers: “First 50 customers get a free upgrade.”

Because these offers can create binding obligations, it’s important that your wording is accurate and your conditions are realistic. In New Zealand, you also need to keep consumer and advertising rules in mind - especially the Consumer Guarantees Act 1993 and the Fair Trading Act 1986, which broadly prohibit misleading or deceptive conduct and false or misleading representations in trade or commerce.

What Is A Bilateral Contract In New Zealand?

A bilateral contract is what most people think of as a “standard” contract. It’s where both parties exchange promises.

For example: you promise to deliver services, and the customer promises to pay. Or a supplier promises to deliver goods, and you promise to pay by a certain date. Both sides take on obligations from the moment the agreement is formed.

How Acceptance Works In A Bilateral Contract

In bilateral contracts, acceptance usually happens through:

• Signing a written agreement;
• Confirming in writing (including email) that you accept the terms;
• Conduct that clearly shows agreement (for example, issuing a purchase order that’s accepted and fulfilled).

While written contracts are often best for clarity, not every bilateral contract needs to be a formal document - but relying on informal arrangements can make disputes harder to resolve later.

Everyday Business Examples Of Bilateral Contracts

• Client service agreements: You deliver a service, the client pays.
• Supplier agreements: A supplier delivers stock, you pay under agreed terms.
• Leases: You pay rent, the landlord grants you the right to occupy premises (plus other obligations on both sides).
• Employment relationships: An employee agrees to work, you agree to pay wages and provide agreed conditions (and comply with employment law).

If you’re hiring staff, a clear Employment Contract is a classic example of a bilateral contract - and it’s one of the most important documents to get right from day one.

Unilateral Vs Bilateral Contracts In New Zealand: What Are The Key Differences?

When people compare unilateral vs bilateral contracts in New Zealand, they’re usually trying to answer one practical question: “What have we actually agreed to, and how can I enforce it?”

Here’s a simple way to compare them.

1. Who Makes Promises?

• Unilateral: Only one party makes a promise (“We will do/pay/give X if you do Y”).
• Bilateral: Both parties make promises (“We will do X and you will do Y”).

2. How Is The Contract Accepted?

• Unilateral: Acceptance happens by performance (doing the thing).
• Bilateral: Acceptance happens by agreement (signing, confirming, or clearly accepting the offer).

3. When Do Obligations Start?

• Unilateral: The party making the promise is generally obligated once the other party completes the required act (and in some cases, once they begin performance in reliance on the offer, withdrawal may not be possible).
• Bilateral: Both parties become obligated once the agreement is formed (even before performance happens).

4. Where Do They Commonly Show Up In Business?

• Unilateral: Promotions, rewards, public offers, referral incentives, “money-back guarantees”.
• Bilateral: Service agreements, supply agreements, leases, employment agreements, software licences, shareholder arrangements.

5. What’s The Usual Legal Risk?

Unilateral contract risks often involve unclear wording, hidden conditions, or operational inability to deliver what was promised. If the offer is misleading, you can also create compliance issues under consumer and fair trading rules (including the Consumer Guarantees Act 1993 and the Fair Trading Act 1986).

Bilateral contract risks often involve unclear scope, unclear payment terms, missing termination rights, liability exposure, and disputes about variations (“we agreed to change it” versus “no we didn’t”). This is why it’s usually worth having a properly drafted Service Agreement (or terms and conditions) instead of relying on informal emails and templates.

Are Unilateral And Bilateral Contracts Legally Enforceable In New Zealand?

Yes - both unilateral and bilateral contracts can be enforceable in New Zealand, as long as the core elements of a contract are present and the terms aren’t illegal or contrary to public policy.

While contract law can get technical, the “building blocks” you should think about are:

• Offer: One party proposes clear terms.
• Acceptance: The other party accepts (by performance in unilateral contracts, or agreement in bilateral contracts).
• Consideration: Something of value is exchanged (money, goods, services, a promise, etc.).
• Intention to create legal relations: In business settings, this is usually assumed.
• Certainty of terms: The agreement must be clear enough to enforce.

Why Certainty Matters (Especially For Unilateral Offers)

Unilateral offers can run into trouble if they’re vague, inconsistent, or missing key conditions. For example:

• If your promo doesn’t explain eligibility clearly, you may end up arguing over who qualified.
• If your “guarantee” doesn’t state limits, you can end up with refund expectations you didn’t price for.
• If your staff interpret the offer differently in-store versus online, you can create disputes and reputational damage.

For consumer-facing offers, your broader legal compliance also matters. If you sell goods or services to consumers, the Consumer Guarantees Act 1993 and the Fair Trading Act 1986 may apply and can create consumer guarantees in many situations that can’t be excluded. So even if your “offer” says one thing, consumer law may override parts of it.

Written Vs Verbal Contracts

A contract doesn’t always need to be written to be enforceable. But from a business owner’s perspective, written contracts reduce disputes because they capture the deal clearly and help prove what was agreed.

If you operate online (or collect customer information), it’s also common to use website legal documents as part of your contracting process - like having customers accept online terms at checkout. In that case, your Privacy Policy and your terms should line up with how you actually handle personal information under the Privacy Act 2020.

Common Business Scenarios: Which Type Of Contract Are You Actually Using?

In day-to-day operations, it’s not always obvious whether your arrangement is unilateral or bilateral. Here are some common small business scenarios and how they usually work.

Quotes And Estimates

A quote can be part of forming a bilateral contract, but whether it’s binding depends on the wording and the surrounding context. If you send a quote that’s accepted, you may have a binding agreement about price and scope.

To avoid misunderstandings, make sure your quote clearly states:

• what’s included (and excluded);
• how long the quote is valid for;
• payment terms and timing;
• what happens with variations.

For many businesses, it’s cleaner to attach (or incorporate) standard terms, or use a tailored service agreement structure.

Refund Policies And Guarantees

A “money-back guarantee” can operate like a unilateral offer: “If you’re not satisfied and you follow these steps, we’ll refund you.”

The key is that:

• the conditions must be clear;
• the process must be practical for your team to follow; and
• it must not conflict with consumer law obligations (for example, you can’t mislead customers about their rights under the Consumer Guarantees Act 1993).

Supplier Deals And Purchase Orders

Supplier relationships are usually bilateral contracts (even if they begin informally). Where it gets messy is “battle of the forms” situations - where:

• you send a purchase order with your terms,
• the supplier sends an invoice with their terms, and
• both sides assume their terms apply.

It’s worth getting clarity early on, especially for higher value supply, long-term relationships, or critical stock.

Online Offers, Promotions, And Referral Programs

These often look like unilateral contracts (perform X and receive Y), but they can quickly become complicated if your terms don’t cover:

• time limits and stock limits;
• eligibility criteria;
• fraud or misuse;
• your right to cancel or vary the promo (and when).

If you run competitions or giveaways, you may also want proper competition terms and conditions so your offer is clear and consistently applied.

Business Ownership And Investment Arrangements

Once you’re dealing with co-founders, shareholders, or investors, you’re almost always in bilateral (or multi-party) contract territory - with higher stakes. This is where documents like a Shareholders Agreement and Company Constitution help reduce the risk of disputes about decision-making, funding, exits, and share transfers.

How Do You Draft Better Business Agreements (And Avoid Disputes)?

Understanding unilateral vs bilateral contracts is a great start - but the real value comes from using that knowledge to tighten up how your business makes offers and enters agreements.

Here are practical ways to protect your business from day one.

1. Be Clear About Whether You’re Making An “Offer” Or Just Marketing

Many disputes come from business owners accidentally making a legally enforceable offer (especially in advertising).

If you don’t want to be bound, you need to be careful with wording. For example:

• “Subject to availability” might help, but it shouldn’t be used as a blanket excuse if the overall ad is misleading.
• If you’re setting conditions (like time limits or eligibility), make them prominent and consistent.

This is particularly important under the Fair Trading Act 1986, which is aimed at preventing misleading or deceptive conduct in trade or commerce.

2. Put Your Key Terms In Writing (Especially For Bilateral Deals)

Even if you have a good relationship with a client or supplier, writing down the deal protects both sides.

At a minimum, your written terms should cover:

• scope of work / deliverables;
• pricing and payment terms;
• timelines and dependencies (what you need from the other party);
• variations and change requests;
• confidentiality and IP ownership;
• termination rights;
• liability limits (where appropriate).

This is often done through a properly drafted service agreement, or well-structured website/online terms depending on how you sell.

3. Watch Out For “Acceptance By Conduct”

In business, you can sometimes accept terms by what you do - not just what you sign. Whether conduct amounts to acceptance depends on the circumstances (including whether you clearly objected to the terms and what both sides did next).

For example:

• If you start performing services after receiving a client’s terms, you may be treated as having accepted them.
• If you pay an invoice that states additional fees and you don’t object, you may be seen as accepting those fees (depending on the facts).

If a contract is important to your business, it’s worth pausing and confirming the governing terms before performance begins.

4. Make Sure Your Agreements Match How Your Business Actually Operates

A common trap is using a generic template that doesn’t match your real workflows.

For instance:

• Your promo terms say “online only” but your staff are honouring it in-store.
• Your payment terms say “7 days” but your finance process invoices monthly.
• Your cancellation terms don’t reflect your booking system and lead times.

Misalignment like this isn’t just inconvenient - it can make it harder to enforce your terms consistently.

5. Get Legal Advice For Higher-Risk Or Higher-Value Arrangements

Some agreements are worth getting reviewed or drafted properly because the downside risk is high. This often includes:

• long-term supplier arrangements;
• exclusive deals;
• licensing and IP-related contracts;
• business sales and purchases;
• co-founder and shareholder arrangements;
• contracts involving personal data or sensitive information.

As your business grows, the “handshake deal” approach tends to break down - not because people become difficult, but because expectations, workloads, and money involved all scale up.

Key Takeaways

• Unilateral contracts involve one party promising something in exchange for the other party performing an act (acceptance happens through performance).
• Bilateral contracts involve both parties exchanging promises (acceptance usually happens through agreement, including signing or confirming terms).
• In the New Zealand context, the biggest business risks are usually unclear wording, accidental acceptance, and mismatched expectations.
• Consumer-facing unilateral offers (like promotions and guarantees) need to be carefully worded so they’re clear, achievable, and compliant with the Consumer Guarantees Act 1993 and the Fair Trading Act 1986.
• Bilateral contracts should clearly cover scope, price, payment terms, variations, termination rights, and liability - especially for ongoing client and supplier relationships.
• Using tailored agreements (rather than generic templates) helps you stay protected from day one and reduces disputes as your business grows.

This article is general information only and does not constitute legal advice. Specific advice should be obtained for your circumstances.

If you’d like help reviewing or drafting a business agreement - whether it’s a promotion, a service agreement, or the contracts that sit behind your operations - you can reach us at 1800 730 617 or team@sprintlaw.com.au for a free, no-obligations chat.