How Do You Challenge an ATO Amended Assessment Based on Section 100A?

You open the envelope. Amended assessment. Section 100A. The trustee is now taxed at 45% on distributions made to adult children three years ago. The amount is six figures. Your client wants to know what you’re going to do about it.

This is not a theoretical tax question anymore. This is a dispute.

And the first thing you need to understand is this: challenging a section 100A assessment is not like objecting to a Capital Gains Tax calculation error or a deduction denial. The ATO is making a factual and purposive allegation about how your client structured their family trust distributions. They are saying there was a reimbursement agreement, a tax avoidance purpose, and arrangements that fall outside ordinary family or commercial dealings.

Responding effectively means understanding what the ATO needs to prove, what evidence undermines their position, and how to frame your client’s story in a way that holds up under scrutiny.

This article walks you through the practical steps of challenging a section 100A assessment, from the day the notice arrives to deciding whether to take the fight to the Administrative Appeals Tribunal or Federal Court.

What a Section 100A Amended Assessment Actually Does

When the ATO applies section 100A, they are disregarding a beneficiary’s present entitlement to trust income and instead taxing the trustee on that income at the top marginal rate, currently 45%.

The effect is brutal.

Instead of your client’s adult child (who may have been on a low marginal rate or using losses) being taxed on the distribution, the trustee is hit with the highest possible rate. No tax-free threshold. No personal deductions. Just 45% of the distributed amount.

The ATO will usually apply this to multiple income years if they identify a pattern. So what starts as a single year issue often expands into three, four, or five years of amended assessments. Each one compounds the liability.

On top of the tax itself, you are looking at:

• General interest charge (GIC) running from the original due date of each amended assessment
• Administrative penalties, which the ATO will often impose at 25% or 50% of the tax shortfall depending on their view of your client’s conduct (lack of reasonable care, recklessness, or something in between)
• A debt that starts accruing more interest from the date of the amended assessment notice

If your client does not act quickly, the debt grows. If they pay under protest and lose the dispute, they may be out of pocket for years waiting for a refund. If they do not pay and cannot negotiate a payment arrangement, the ATO can pursue director penalty notices, garnishee orders, or other debt recovery action.

This is why the first 30 days after the amended assessment lands are so important.

First 30 Days: What You Should Do When the Notice Arrives

The clock starts the day your client receives the amended assessment notice. You do not get extra time to think about it.

Here is what needs to happen in the first 30 days.

Check the objection deadline

For most taxpayers, you have two years from the date of the notice to lodge an objection. If the assessment was issued for an income year more than four years old, or if the ATO is alleging fraud or evasion, different rules apply.

Do not assume. Check the notice. Confirm the date it was issued and calculate your deadline. Put it in your diary with multiple reminders. Missing this deadline can be fatal to your dispute.

Understand what years are affected

Section 100A assessments rarely involve a single year. The ATO will usually issue amended assessments for every year they believe the same arrangement applied.

You need to:

• Identify which income years are caught
• Work out whether there are related issues in those years (Division 7A loans, unpaid present entitlements, other trust or corporate adjustments)
• Assess whether the ATO’s factual narrative is consistent across all years, or whether some years are more defensible than others

Some disputes are won or narrowed by showing the ATO has misunderstood the facts in particular years, or by demonstrating that what happened in Year 1 was different to what happened in Year 3.

Identify the ATO’s factual position

The amended assessment notice will usually be accompanied by a position paper or audit report. This document tells you what the ATO believes happened.

Read it carefully. The ATO will set out:

• The distributions they say triggered section 100A
• The alleged reimbursement agreement (how they say funds were redirected or benefits flowed to someone other than the beneficiary)
• Why they believe there was a tax reduction purpose
• Why they say the arrangement falls outside ordinary family or commercial dealings

This is the story you need to dismantle or reframe. You cannot do that unless you understand exactly what they are alleging.

Assess immediate debt and payment issues

If your client cannot pay the amended assessment in full, you need to deal with that reality now.

Options include:

• Applying for a payment arrangement with the ATO while the objection is on foot
• Paying a portion under protest to stop some of the GIC accrual
• In some cases, seeking a stay of recovery proceedings (rare, but possible if there are strong grounds to believe the assessment is wrong)

Do not let debt management derail your dispute strategy. The two issues run in parallel, and both need attention.

Understanding the ATO’s Section 100A Position

The ATO must prove four elements to sustain a section 100A assessment:

If any one of these elements fails, the section 100A assessment should not stand.

Your job is to identify which element (or elements) is weakest in your client’s case, and build your objection around that.

The reimbursement agreement

This is the foundation of every section 100A case. The ATO must show there was an agreement, arrangement, or understanding under which:

• A beneficiary was made presently entitled to trust income, but
• The economic benefit of that income flowed (or was expected to flow) to someone else

“Agreement” is defined broadly. It does not require a written contract. It does not even require both parties to articulate it. The ATO will infer an agreement from conduct, patterns of behaviour, financial flows, and the broader context.

Common fact patterns the ATO relies on:

• Distributions made to adult children with low incomes or tax losses, but the funds remain in the trust and are used for the benefit of parents or a family business
• Beneficiaries “gifting” or “lending” their entitlements back to the trust or to other family members immediately after year-end
• Circular flows of funds (beneficiary is made presently entitled, funds are transferred out, then loaned or paid back in a way that benefits someone else)

What the ATO is looking for is a disconnect between legal entitlement and economic benefit. If that disconnect appears deliberate and structured to reduce tax, they will call it a reimbursement agreement.

A benefit to another person

This element asks: did someone other than the named beneficiary actually obtain the benefit of the distribution?

The ATO will trace funds. They will review:

• Bank statements
• Loan agreements (or the absence of them)
• How the entitlement was recorded in the beneficiary’s accounts
• Whether the beneficiary had control over the funds or whether someone else directed their use

If the funds were used to reduce a family company’s debts, fund the parents’ lifestyle, or capitalise another entity, the ATO will argue the benefit went elsewhere.

You need to be ready to explain, with evidence, what happened to the money and why that was consistent with the beneficiary genuinely receiving and controlling their entitlement.

Tax reduction purpose

The ATO does not need to prove tax avoidance was the only purpose. They only need to show it was one of the purposes.

This is a low bar for the ATO and a hard one for taxpayers to clear.

The ATO will look at:

• The marginal tax rates of the parties involved (e.g. distributions to a beneficiary on a low rate, benefit to someone on a high rate)
• The timing of the arrangement (was it implemented just before year-end?)
• Whether there were tax losses or franking credits in play
• Adviser file notes, emails, and any contemporaneous documents that discuss tax outcomes

If your adviser files contain emails saying “this structure will save $50,000 in tax”, you have a problem. If there is no commercial explanation for why the beneficiary was chosen other than tax, you have a problem.

But if you can show there were genuine family, succession, or commercial reasons for the distribution structure, you start to chip away at the tax purpose allegation.

Ordinary family or commercial dealing exception

This is your best defence in many cases.

Even if the ATO can prove the first three elements, section 100A does not apply if the arrangement was an ordinary family dealing or an ordinary commercial dealing.

The test is objective: would a reasonable person, looking at the arrangement in context, regard it as within the normal course of family or business relationships?

Factors that support the ordinary dealing argument:

• The arrangement was consistent with prior years or longstanding family practices
• The beneficiary had genuine control and autonomy over their entitlement (even if they later chose to help the family business or parents)
• There was a sound non-tax explanation for the structure (e.g. asset protection, succession planning, supporting a family member through financial difficulty)
• The arrangement was documented in a way consistent with genuine commercial or family decision-making, not contrived to manufacture a tax outcome

Factors that undermine it:

• The arrangement was artificial, one-off, or inserted solely for the relevant income year
• There is no evidence the beneficiary made a real decision about their entitlement
• The funds flowed in a way that suggests pre-arrangement rather than genuine autonomy
• The structure was recommended purely to exploit a tax outcome

If you are running an ordinary dealing defence, you need contemporaneous evidence. Trustee minutes. Beneficiary statements. Evidence of family discussions. Anything that shows this was a real decision, not a paper exercise.

Building Your Objection: Facts, Documents, and the Ordinary Dealing Story

An objection to a section 100A assessment is not a theoretical tax essay. It is an evidence-based argument that the ATO has misunderstood or mischaracterised what happened.

That means you need documents.

What contemporaneous evidence to gather

The earlier you gather this material, the better. Ideally, you are doing this during the audit, before the amended assessment is even issued. But if the assessment has already landed, you still need to pull together everything relevant.

Look for:

• Trustee resolutions – What did the trustee minute at the time? Was there a genuine decision-making process, or was the resolution a formulaic tax-time exercise?
• Beneficiary loan agreements or gift deeds – If the entitlement was left outstanding or forgiven, how was that documented? Was interest charged? Were repayment terms genuine?
• Bank statements and transaction records – Where did the money actually go? Can you trace it in a way that supports your narrative, or does it support the ATO’s?
• Family or business context evidence – Emails, board minutes, shareholder agreements, family meeting notes. Anything that shows why the structure made sense outside of tax.
• Adviser file notes and correspondence – What advice was given at the time, and what did it focus on? Be careful here: if the advice was purely tax-driven with no commercial context, it may hurt more than help.
• Prior year tax returns and structures – Can you show consistency over time, or is this a one-off that coincidentally delivered a tax benefit?

If the documents are thin, that does not mean you cannot object. But it does mean your objection will rely more heavily on witness statements and narrative explanation, which are easier for the ATO to dismiss.

How to frame the ordinary dealing story

Your objection needs to tell a clear, plausible story about what happened and why it was ordinary.

Bad version (vague, defensive, unconvincing):

“The distribution to the adult children was part of normal family arrangements and there was no tax avoidance purpose.”

Good version (specific, grounded, evidence-based):

“The trustee distributed income to the adult children consistent with a longstanding family practice of equalising benefits among the next generation. The funds were held on loan to the trust to provide working capital for the family farming business, which had been operated as a trust enterprise for 20 years. The loans were documented, bore interest at commercial rates, and repayment schedules were set by reference to the business’s cash flow. The children had independent financial advice and elected to support the business as part of their long-term succession interest. The tax outcome was incidental to the structure, not its purpose.”

Notice the difference. The good version:

• Explains why the distribution happened (equalisation, succession, family history)
• Explains what happened to the funds and why (working capital, documented loans, commercial terms)
• Addresses the autonomy and decision-making of the beneficiaries (independent advice, genuine choice)
• Positions tax as a byproduct, not the driver

You may not have all these elements. But you need enough of them to construct a credible alternative to the ATO’s “this was a contrived tax arrangement” narrative.

When to bring in specialist tax counsel or valuation experts

Some section 100A disputes turn on technical tax issues that sit at the edge of the law. When is a benefit “obtained” for the purposes of the section? What counts as an “agreement” when there is no express discussion? How do you apply the ordinary dealing test in novel commercial contexts?

If your case involves those kinds of interpretive questions, or if the ATO’s technical reasoning is questionable, you may need a tax silk or senior counsel to settle an opinion or draft parts of the objection.

Similarly, if part of your defence is that the arrangement had genuine commercial value (e.g. the loan back to the trust was on market terms, the asset protection benefits were real, the succession structure was standard for family enterprises), you may need valuation or industry expert evidence to back that up.

Do not bring in experts just to add weight. Bring them in when they can genuinely change the quality of the argument or the evidence.

Lodging an Objection and Managing Penalties and Interest

Once you have gathered your evidence and framed your argument, you need to lodge the objection within the deadline.

What goes into the objection

Your objection should:

• Clearly identify the amended assessment you are objecting to (income year, date of issue, amount)
• State the grounds of objection (which elements of section 100A you say are not made out, or why the ordinary dealing exception applies)
• Set out the facts, supported by evidence
• Address the ATO’s specific reasoning in their position paper
• Explain what outcome you are seeking (full disallowance of the amended assessment, or if you are conceding some issues, be clear about what you are conceding and what you are disputing)

If you are objecting to multiple years, you can lodge a single objection covering all years or separate objections for each year. The approach depends on whether the facts and arguments are the same across all years or whether some years have distinct issues.

Do not lodge a “holding objection” with no detail just to meet the deadline unless you absolutely have to. The ATO is entitled to decide an objection based on what you put in it. If you lodge a bare-bones objection and the ATO disallows it, you will need to rebuild your case at the AAT or Federal Court stage, and you will have lost the opportunity to settle early.

That said, if you are up against the deadline and still gathering evidence, lodge what you have and clearly flag that further material will follow. You can request an extension of time to provide additional submissions, but do not assume the ATO will grant it.

Challenging penalties separately

The ATO will usually impose administrative penalties on top of the section 100A tax shortfall. The penalties are calculated as a percentage of the shortfall and depend on the ATO’s view of your client’s behaviour:

• Failure to take reasonable care: 25%
• Recklessness: 50%
• Intentional disregard: 75%

You can object to the penalty separately from the tax, and you can seek remission even if you end up conceding the underlying section 100A issue.

Grounds for penalty remission include:

• Your client relied on professional advice (if the advice was competent and the client fully disclosed all relevant facts)
• The section 100A issue was legally uncertain at the time (there was no clear ATO guidance, or the law was still being worked out in the courts)
• Your client took reasonable care in their tax affairs, and the error was not due to carelessness or neglect

Penalties are often the most negotiable part of a section 100A dispute. The ATO may hold firm on the tax but agree to reduce or remit penalties if you can show genuine engagement and reasonable care.

Dealing with payment and debt while the objection is on foot

The objection does not stop the debt. The amended assessment is legally payable, and interest continues to accrue.

Your options:

• Pay the amount in full under protest and claim a refund if you win. This stops GIC accruing, but ties up cash.
• Negotiate a payment arrangement with the ATO. This keeps the debt manageable but does not stop interest.
• In rare cases, apply to the ATO or court for a stay of recovery proceedings. This is only realistic if you have very strong grounds to believe the assessment is wrong and paying would cause serious hardship.

Most clients cannot afford to pay the full amount upfront. That is fine. Just make sure you have a plan to manage the debt while the dispute runs, and make sure your client understands that even if they win, it may take 12 to 24 months to resolve.

If the Objection Fails: AAT or Federal Court?

The ATO has disallowed your objection. Now what?

You have 60 days from the date of the objection decision to either:

• Apply for review by the Administrative Appeals Tribunal (AAT), or
• Appeal to the Federal Court

Which path you choose depends on the nature of your dispute, the amount at stake, and the kind of fight you are in.

AAT review: merits-based, evidence-focused

The AAT is a merits review body. It reconsiders the ATO’s decision afresh. You can run new evidence, call witnesses, cross-examine ATO witnesses, and argue both the facts and the law.

For section 100A disputes, the AAT is often the right forum because:

• Section 100A cases are intensely fact-dependent (was there a reimbursement agreement? Did the beneficiary have real control? Was this an ordinary dealing?)
• You will likely need to lead evidence from your client, family members, the trustee, and possibly advisers
• The AAT is less formal and less expensive than Federal Court, though still a significant commitment

The downside of the AAT is that the Tribunal’s decision on pure questions of law can be appealed to the Federal Court by either party. So even if you win at the AAT, the ATO can appeal if they disagree with the Tribunal’s interpretation of section 100A.

Federal Court: legal questions, judicial authority

If your dispute turns on a point of law, the correct interpretation of “reimbursement agreement”, whether a particular fact pattern can constitute an ordinary dealing, the scope of the tax purpose test, the Federal Court may be the better option.

The Federal Court is a superior court. Its decisions set binding precedent (subject to appeal to the Full Federal Court or High Court). If you win, the ATO is bound by that decision for future cases.

But Federal Court proceedings are more expensive, more formal, and more procedurally rigid than the AAT. You will need barristers, extensive written submissions, and a disciplined approach to evidence. If your case is fact-heavy and does not turn on a clean legal issue, the Federal Court can be a harder environment to navigate.

Practical factors that influence the choice

How much is at stake? If the liability is modest and the facts are messy, the AAT is usually the better value. If the liability is large or the legal question has broader implications for your client’s group structure, Federal Court may be justified.

What does success look like? If you are looking for a complete vindication on the facts, the AAT gives you the best chance to run a full evidentiary case. If you are looking to set a precedent or force the ATO to reconsider its approach, the Federal Court carries more weight.

What is your client’s risk tolerance? Federal Court proceedings are high-stakes, high-cost, and slower. AAT is faster and more flexible, but there is always the risk of an ATO appeal if you win on a contentious legal point.

There is no right answer for every case. But by the time you are making this decision, you should have litigation lawyers in the room helping you assess the options.

Common Patterns We See in Section 100A Disputes

Every section 100A case has its own facts. But certain patterns emerge repeatedly, and knowing them helps you identify where your case sits and what arguments are likely to work.

Adult children beneficiaries, parents benefit

The classic scenario. Trust distributes income to adult children who are on low marginal rates or have carried-forward losses. The funds remain in the trust or are loaned back, and they are used to fund the parents’ business, reduce director loans, or support the family’s lifestyle.

The ATO will almost always argue this is a reimbursement agreement with a tax purpose. Your defence depends on showing:

• The children had genuine control and made a real decision to support the family enterprise
• The arrangement was consistent with longstanding family practices or succession planning
• The loans or benefits were documented and genuine, not shams

If you can point to years of similar distributions, independent advice to the children, and a credible explanation for why they supported the business, you can sometimes land this in the ordinary dealing zone.

If it was a one-off tax-time decision with no context, you are in trouble.

Loss company or trust as beneficiary

Income is distributed to a company or trust with tax losses, which shelters the income. The funds are then used elsewhere in the group, often by entities or individuals with no losses.

This is high-risk for section 100A, particularly if the loss entity has no genuine business activity or the structure was created solely to absorb the distribution.

The ATO’s argument is straightforward: the distribution was structured to reduce tax by routing income through a loss entity, and the economic benefit went elsewhere.

Your defence turns on whether the loss entity had a genuine business or investment purpose, whether the funds were used for that purpose, and whether the distribution was made for reasons other than tax (e.g. capitalising the loss entity to resume trading, equalising interests in a family group).

If the loss entity is a shelf company with no history and no function other than absorbing income, you will struggle.

Unpaid present entitlements and circular arrangements

Beneficiary is made presently entitled. The entitlement sits unpaid. It is later forgiven, capitalised, or converted to a loan back to the trust. The funds are used by the trustee or another family member.

The ATO will argue the entitlement was never intended to be paid, the beneficiary never had real control, and the arrangement was contrived to create a deduction or loss in a later year (via the forgiveness or write-off) or to keep the funds in the trust while avoiding Division 7A.

Your defence requires showing the unpaid entitlement was genuine (beneficiary could call for payment, had a real debtor/creditor relationship with the trust), and the decision to forgive or convert it was made for sound family or commercial reasons, not to engineer a tax result.

If the entitlement was created solely on paper, never discussed with the beneficiary, and forgiven automatically the next year, you have a weak case.

Late-stage audit escalation

Sometimes the ATO conducts a routine trust review, gathers extensive information, and only raises section 100A late in the piece. By the time you realise section 100A is on the table, you have already provided documents and explanations that may not have been framed with section 100A in mind.

If this happens, you need to:

• Review everything you provided during the audit and assess whether any statements or documents undercut your defence
• Clarify (in writing) any factual assumptions the ATO has made that are incorrect
• Provide additional context and evidence that supports an ordinary dealing narrative

You cannot “take back” what you said during the audit, but you can frame it differently and fill in gaps the ATO may have missed.

Working with Your Client and Your Adviser Team

A section 100A dispute is not a solo project. It requires coordination between the accountant (who knows the tax history and client relationship), tax counsel (who can frame the technical arguments), and litigation specialists (who understand evidence, process, and how disputes actually resolve).

Who does what

The accountant typically:

• Gathers the financial and trust records
• Explains the history of the structure and the commercial context
• Manages the client relationship day-to-day
• Coordinates the overall response and ensures deadlines are met

Tax counsel typically:

• Advises on the technical merits of the section 100A argument
• Settles the objection or key submissions
• Provides opinions on prospects of success and litigation risk

Litigation lawyers typically:

• Manage the dispute process (objection, AAT, Federal Court)
• Handle evidence gathering, witness preparation, and procedural strategy
• Run the hearing if the matter goes to review or appeal
• Negotiate settlement with the ATO at all stages

The key is knowing when to bring each specialist in. You do not need a litigation team on day one if the matter is likely to settle at objection. But if the ATO disallows the objection and you are heading to the AAT, you need disputes experience in the room.

How to help clients decide when to settle

Not every section 100A dispute should be fought to the end. Some settle because the client cannot afford the cost or risk of a hearing. Some settle because the ATO offers a pragmatic compromise (e.g. partial concession on the tax, remission of penalties). Some settle because the facts or law turn out to be weaker than expected once you dig into the evidence.

Your job is to help your client make an informed decision at each stage. That means:

• Being honest about the strengths and weaknesses of the case
• Giving realistic cost estimates for each stage (objection, AAT, Federal Court)
• Explaining what settlement might look like and whether the ATO is likely to negotiate
• Helping the client understand the non-financial costs (time, stress, management distraction, reputational risk if the matter becomes public)

Some clients want to fight on principle. Some want certainty and closure. Some want to recover their costs as quickly as possible. There is no right answer, but the decision should be made with full information, not hope or frustration.

What Happens Next

If you are staring at a section 100A amended assessment, you are not powerless. But you need to act quickly, strategically, and with the right team around you.

Gather your evidence. Frame your story. Lodge a proper objection. Do not hope the ATO will back down without a fight, but do not assume litigation is inevitable either. Many section 100A disputes settle if you can show the ATO’s factual assumptions are wrong or that the arrangement genuinely falls within ordinary dealings.

And if settlement is not possible, be prepared to take the fight to the AAT or Federal Court. Section 100A is not settled law. The ATO’s interpretation is still being tested in the courts, and well-run cases with strong facts can succeed.

Litigation is not the enemy. Poor preparation is.

If you need help responding to a section 100A assessment, or if you are already in the objection or review process and need strategic advice, we can help. Aptum specialises in commercial and tax disputes. We work with accountants, tax advisers, and clients to challenge assessments, manage objections, and run cases through the AAT and Federal Court when necessary.

Reach out. Let’s talk about what the ATO is alleging, what your options are, and what the pathway forward looks like.

Disclaimer: This article provides general information only and does not constitute legal advice. Section 100A disputes are highly fact-specific, and the right response depends on your individual circumstances. You should seek specialist tax and legal advice before taking any action in response to an ATO amended assessment.