Joint ABN Options for Australian Co-Founders

When you’re starting a business with someone else, it’s natural to look for the simplest way to “share” the admin. One of the most common questions we hear from co-founders is: can we get a joint ABN?

The short answer is that a “joint ABN” isn’t really a separate category in the Australian system. But you can run a business together under one ABN - you just need to choose the right structure and set things up properly from day one.

In this guide, we’ll explain what people usually mean by a joint ABN, what your actual options are, and what legal documents you should consider to protect your co-founder relationship (and the business you’re building together).

What Is A Joint ABN (And Does It Exist In Australia)?

In everyday conversation, a “joint ABN” usually means:

• two (or more) people are running one business together; and
• they want to invoice customers and operate under one ABN; and
• they want the ABN to “belong” to both of them.

In Australia, an Australian Business Number (ABN) is issued to an entity, not to a casual arrangement.

That entity might be:

• a sole trader (an individual)
• a partnership
• a company
• a trust (with a trustee)
• an incorporated association

So while “joint ABN” isn’t an official ABN type, you can achieve a similar outcome by choosing an entity that can have more than one owner or controller (most commonly a partnership or a company).

The key is this: the structure you choose determines what “sharing” an ABN means legally - including who is responsible for tax, debts, contracts, and what happens if things go wrong.

When Do People Want A Joint ABN?

There are a few typical scenarios where founders go looking for a joint ABN.

You’re Starting A Business With A Friend Or Family Member

You might be splitting work and costs, sharing clients, and planning to grow together - but you don’t want (or don’t think you need) a company yet.

You’re Co-Founders Building A Startup

You might be developing a product, pitching to customers or investors, and signing up suppliers. In this context, the ABN is usually part of a bigger question: what structure will set you up for growth and investment?

You’re Doing A Joint Project Or Side Hustle

Sometimes it’s a short-term collaboration: a joint event, a temporary service offering, or a single contract. You may still want to invoice under one ABN for simplicity.

You’re Trying To Avoid Admin Or Costs

It’s common to think “we’ll just use one person’s ABN for now,” especially when you’re testing demand. The issue is that this can create hidden risk - including tax issues, disputes about ownership, and uncertainty about who is legally responsible.

If you’re operating together, it’s worth taking a step back and choosing a structure that matches what you’re actually doing.

Your Main Options Instead Of A Joint ABN

To run a business together under one ABN, you typically have three practical pathways. Which one is right depends on how you want to share ownership, risk, and decision-making.

Option 1: One Person’s ABN (Sole Trader) - Usually Not Ideal For Co-Founders

This is where one co-founder registers as a sole trader and uses their ABN for the business, even though both people are contributing.

This approach can feel easy in the beginning, but it often causes problems, because legally:

• the sole trader is the one contracting with customers and suppliers
• the sole trader is generally responsible for business debts and liabilities
• income is earned by that individual (even if you “split” it informally)
• the other person’s rights to the business can be unclear

If the relationship breaks down, it can become a dispute about who “owns” the clients, brand, accounts, and goodwill - and whether the other person was an employee, contractor, or informal partner.

If you’re going to start this way while validating an idea, it’s a good idea to put the key points in writing early (even a simple agreement), then transition to a better structure when the business proves itself.

Option 2: A Partnership ABN - The Closest Thing To A “Joint ABN”

If you and your co-founder want one ABN that is connected to both of you, a partnership is often what you’re actually looking for.

A partnership is generally an arrangement where two or more people carry on business together, with a view to profit. Importantly, partnerships can sometimes arise unintentionally based on how you operate - even if you never formally “set one up”.

In a partnership:

• the partnership can have its own ABN (separate from each partner’s individual ABNs)
• partners share profits (and often control) based on what you agree
• each partner may be personally liable for partnership debts (this is a major point)

Partnerships can work well for some small businesses, particularly where:

• you want a simpler structure than a company
• you’re comfortable with shared personal risk
• the business is not planning to raise investment in the near term

Even if you trust each other completely, a proper Partnership Agreement is essential. It’s not just about preventing arguments - it’s about setting clear rules for what happens when circumstances change (new opportunities, new partners, life events, or a breakup between founders).

Option 3: A Company ABN - Often The Best Option For Growth And Risk Management

If you set up a company, the company is a separate legal entity. That company can hold an ABN, enter contracts, own assets, and hire staff.

This is often attractive to co-founders because:

• ownership is clearer (via shares)
• responsibility is clearer (the company contracts, not you personally - though directors and shareholders can still be exposed in some situations, including through personal guarantees and certain director duties)
• it’s easier to bring in investors (compared to informal arrangements)
• it can help protect personal assets (limited liability generally applies to shareholders, but it’s not absolute - for example, personal guarantees, insolvent trading and other director obligations can still create personal exposure)

Companies come with extra admin and compliance, but for many co-founder businesses, the clarity is worth it.

If you set up a company, you’ll usually also want a Company Constitution (or rely on replaceable rules) and, in many cases, a Shareholders Agreement to properly document how you’ll run the business together.

Key Legal And Tax Issues To Think About Before You “Share” An ABN

When you’re choosing the structure behind your joint ABN setup, you’re not just deciding how to invoice. You’re deciding how the law will treat your relationship, your risk, and your rights.

Who Owns The Business (And The Brand)?

Ownership can mean different things:

• Who owns the business name and domain?
• Who owns the social media accounts and marketing assets?
• Who owns the customer list and goodwill?
• Who owns equipment, stock, or IP created during the relationship?

In a partnership, these points can become messy if they’re not clearly agreed. In a company, ownership is typically more straightforward, because the company can own assets and IP, and each founder’s stake is reflected in their shares.

Who Is Liable If Something Goes Wrong?

This is one of the biggest “hidden” issues with a joint ABN approach.

Depending on the structure, liability might fall on:

• one individual (if you’re using one person’s sole trader ABN)
• all partners personally (in a partnership, often jointly and severally)
• the company (in a company structure, subject to exceptions like personal guarantees, director duties, and insolvency-related obligations)

If your business gives advice, provides services, sells products, or has safety risks, liability is not theoretical - it’s part of everyday operations.

How Will You Split Profits (And Handle Losses)?

It’s common for co-founders to say “we’ll do 50/50,” but profit-sharing is only one part of the picture.

You should also think about:

• what counts as business expenses
• whether founders are paid wages or drawings before profits are split
• how you’ll fund the business if it needs extra cash
• what happens if one founder does significantly more work than the other

Clarity here can prevent serious disputes later - especially once money starts moving regularly.

GST, Invoicing, And Ongoing Compliance

ABN decisions often sit alongside tax and compliance obligations.

For example, depending on your turnover and activities, you may need to register for GST and issue compliant tax invoices. You should also make sure you’re recording income and expenses accurately and consistently from the start.

We won’t dive into tax advice here (your accountant is your best first point of contact), but the key legal point is: your ABN and business structure should match what you’re actually doing, not just what’s convenient this week.

What Legal Documents Should Co-Founders Have When Operating Under One ABN?

Once you decide the right setup for your “joint ABN” approach, the next step is making sure your business is protected with the right legal documents.

Not every business will need every document below, but these are the most common ones we recommend co-founders consider.

• Partnership Agreement: If you’re operating as a partnership, a Partnership Agreement can set out ownership, profit split, roles, decision-making, what happens if someone wants to leave, and how disputes are handled.
• Shareholders Agreement: If you’ve set up a company, a Shareholders Agreement is one of the best ways to protect both the business and the relationship, especially around deadlocks, exit rights, and bringing in new shareholders.
• Company Constitution: A Company Constitution helps set the rules for how the company is run (and is often used alongside a shareholders agreement).
• Service Agreement Or Customer Contract: If you provide services (consulting, trades, creative work, professional services), a Service Agreement can help set expectations around scope, fees, timing, liability, and what happens if the client relationship goes off track.
• Website Terms And Conditions: If you operate online (even if you’re not eCommerce), Website Terms and Conditions can set the rules for using your site and help manage legal risk around content and customer interactions.
• Privacy Policy: If you collect personal information (think: email addresses, enquiries, bookings, mailing lists), a Privacy Policy explains how you collect, use, and store that data - and it’s a common compliance requirement for Australian businesses operating online.

One practical tip: if you’re co-founders, it’s worth agreeing early on who signs contracts and what approval is needed for big decisions (like hiring staff, signing a lease, or taking on debt). Even if you trust each other, having a clear process can prevent misunderstandings.

Common Joint ABN Mistakes (And How To Avoid Them)

Most joint ABN problems don’t start with bad intentions. They start with founders moving quickly, relying on trust, and putting off the paperwork.

Here are some of the most common traps we see.

Using One Founder’s ABN “Just For Now”

This can create a mismatch between what you think the relationship is and what it looks like legally. If invoices, bank accounts, and contracts are all in one person’s name, it can be hard to prove the other founder has ownership rights later.

If you truly need a short-term solution while testing your idea, at least document the basics (who owns what, who’s doing what, and how income is split), then move to a partnership or company when the business gains traction.

Not Being Clear On Roles And Decision-Making

Co-founders often divide work informally: “you do sales, I do ops.” But what happens if:

• you disagree on pricing?
• one founder wants to reinvest profits and the other wants distributions?
• one founder wants to pivot the business model?

Your agreement should cover how decisions are made and what happens if you hit a deadlock.

Skipping The Exit Plan

It can feel uncomfortable to talk about “breakups” when you’re excited about the business. But this is exactly why you should plan early.

Good exit planning can cover:

• what happens if a founder leaves voluntarily
• what happens if someone can’t contribute due to illness or other commitments
• how shares or partnership interests are valued
• who can buy the other person out (and on what terms)

It’s much easier to agree on fair rules when things are going well than when there’s a dispute.

Forgetting About Customer-Facing Legal Risk

Many joint ABN conversations focus on who “owns” the ABN, but the bigger operational risks are often customer-related: complaints, refunds, scope disputes, late payments, and liability claims.

Solid customer terms (and the right structure behind them) can make a major difference in how manageable those issues are.

Key Takeaways

• A “joint ABN” isn’t a formal ABN type in Australia, but you can operate together under one ABN by choosing the right entity (commonly a partnership or a company).
• Using one person’s sole trader ABN for a shared business can create major risks around ownership, tax, and liability.
• A partnership ABN is often the closest option to what people mean by a joint ABN, but partnerships can sometimes arise unintentionally and partners can be personally liable for debts, so the structure needs careful thought.
• A company ABN can provide clearer ownership (shares) and often better risk management, but limited liability isn’t absolute and personal exposure can still arise (for example through guarantees and certain director obligations).
• Co-founders should seriously consider key legal documents such as a Partnership Agreement or Shareholders Agreement, plus customer contracts and online policies where relevant.
• Getting the structure and paperwork right early can prevent expensive disputes later and help your business grow with confidence.

If you’d like a consultation on setting up your business with a joint ABN-style structure, you can reach us at 1800 730 617 or team@sprintlaw.com.au for a free, no-obligations chat.