Common deduction mistakes that trigger ATO attention
The deduction errors that most often draw scrutiny, from mixed private and business expenses to unsubstantiated claims, and how to keep client claims defensible.
Deductions are where a lot of tax goes right or wrong. Claim too little and the client pays more than they should. Claim too much or without substantiation and you invite scrutiny, amendments, and penalties. Most problem deductions are not aggressive schemes, they are ordinary claims made carelessly. Knowing the common mistakes helps keep every client's return both fair and defensible.
Mixing private and business expenses
The most frequent error is claiming a private expense, or the private portion of a mixed expense, as a business deduction. Phone and internet, motor vehicle, and home-related costs almost always have a private component, and only the business-use portion is deductible. Claiming the full amount when the expense is partly private is a reliable way to draw attention.
The ATO regularly signals the deduction areas it is focused on, and its guidance is published by the ATO. Keeping an eye on those focus areas helps you steer clients away from the claims most likely to be questioned.
Claiming without substantiation
A deduction is only as good as the evidence behind it. Estimated figures, round numbers, and claims with no receipts or logbooks are all warning signs. The rule is simple: if the client cannot substantiate it, it should not be claimed. Encouraging clients to keep records as they go is far easier than reconstructing them at tax time.
- Apportion mixed expenses to the genuine business-use share.
- Substantiate every material claim with records.
- Test the nexus between the expense and earning income.
Missing the connection to income
For an expense to be deductible, there generally has to be a real connection between the expense and earning assessable income. Costs that are private in nature, or too remote from income-earning, do not qualify no matter how genuinely they were incurred. Testing this nexus honestly is part of preparing a defensible return.
Capital versus revenue
Another common slip is claiming a capital expense as an immediate deduction. Something that provides a lasting benefit is often capital in nature and deducted over time rather than in one year, subject to the rules that apply. Getting this distinction right avoids both over-claiming in the current year and missing legitimate deductions in later years.
Build checks into the return process
The way to avoid these mistakes consistently is to build the checks into how returns are prepared. In Finye you can attach a standard review checklist to your return jobs, prompting the preparer to test apportionment, substantiation, and the income connection before the return is finalised. Making these checks routine, rather than relying on individual judgement each time, is what keeps claims defensible across the whole client base. You can see how firms standardise their review steps in Finye's guides.
Educate clients on what they can claim
Many deduction problems start with clients who simply do not know the rules, either claiming things they should not or missing things they could. A short explanation of what makes an expense deductible, and what records are needed to support it, pays off across every future return. Clients who understand the apportionment and substantiation requirements keep better records and ask better questions, which makes the preparer's job easier and the resulting return far more robust if it is ever examined.
Protect the client and the practice
Getting deductions right is not about being conservative for its own sake, it is about claiming everything the client is genuinely entitled to while keeping every claim defensible. A return built on properly apportioned, substantiated, connected deductions holds up under scrutiny. That is the outcome that serves the client best and keeps the practice's own standing intact.