Costly Tax Mistakes: Crazy Deductions and Common Errors for Individuals and Business Owners

By
R J Sanderson & Associates Pty Ltd
Published on 
September 16, 2025
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When Good Intentions Don’t Equal Tax Deductions

In one of the more unusual cases the Australian Taxation Office (ATO) has seen, a taxpayer claimed a $20,000 deduction for feeding and desexing stray cats. Noble? Yes. Deductible? No.

The ATO rejected the claim because it wasn’t linked to the taxpayer’s employment or income. While the individual argued it was a community service, tax law requires deductions to have a direct connection to earning assessable income.

This isn’t an isolated case. Every year, the ATO reveals a long list of questionable and costly mistakes that Australians make when preparing their tax returns. Some are quirky, like claiming pet food. Others are common, such as over-claiming home office expenses

The bottom line? Tax mistakes can cost you thousands in denied deductions, penalties, or audits. In this article, we’ll explore:

  • Real-life “crazy” deductions that didn’t fly
  • The most common errors individuals and business owners make
  • The true costs of getting it wrong
  • How you can avoid making the same mistakes

Why Do Tax Mistakes Happen?

Most people don’t deliberately set out to break tax rules. Mistakes often come from misunderstanding, assumption, or poor record-keeping. Common reasons include:

  • DIY pitfalls – Relying on guesswork or outdated advice when lodging tax returns.
  • Assuming “noble” means deductible – Believing community or personal spending should be rewarded by the ATO.
  • Myths and misinformation – Picking up bad advice from friends, family, or the internet.
  • Overconfidence – Thinking small expenses won’t be noticed by the ATO.
  • Changing rules – Not keeping up with updated tax thresholds, deduction methods, or compliance obligations.

While some mistakes are harmless, others trigger penalties or audits. And once the ATO gets involved, fixing errors becomes far more stressful and costly than doing it right the first time.

Crazy Tax Deductions That Didn’t Fly

Every year, the ATO releases examples of deductions that people have tried — and failed — to claim. While they might make you smile, they also highlight the risk of misunderstanding what the tax law actually allows.

Feeding Stray Cats – $20,000 Deduction

A taxpayer claimed expenses for food and veterinary bills for stray cats. While charitable, there was no link to their income-earning activities. The ATO said no.

Pet Grooming and Food

Unless your pet directly earns income (such as a security dog or performing animal), expenses like food, vet care, and grooming are personal and not deductible.

Gym Memberships and Fitness Costs

Only deductible if your job has a direct requirement to maintain physical fitness — for example, professional athletes or members of the defence force. Office workers can’t claim gym fees as “stress management.”

Daily Coffee and Lunch

Buying coffee on the way to work or lunch at your desk isn’t deductible. These are considered private living costs. Only certain travel-related meals are claimable.

Weddings and Personal Celebrations

One taxpayer attempted to claim wedding reception costs under “client entertainment.” The ATO quickly disallowed the expense, noting the lack of income connection.

School Fees and Tutoring

Parents sometimes try to claim private school fees or tutoring under “education expenses.” Unless directly related to earning income (for example, professional study), these are not deductible.

These examples may sound far-fetched, but they underline a serious point: deductions must always be linked to how you earn your income.

For Individuals

Not every mistake makes headlines. Most are far more ordinary — but equally damaging to your financial position if you get them wrong.

1. Claiming Clothing That Doesn’t Qualify

You can only claim occupation-specific clothing, protective wear, or uniforms with a logo. General work attire (like suits, black pants, or office shoes) is not deductible.

2. Car Expenses Without a Logbook

Claiming large car deductions without a valid logbook or using cents-per-kilometre incorrectly is a red flag. The ATO often checks for over-claims in this area.

3. Overstating Home Internet and Phone Use

If you work from home, you can only claim the work-related portion of internet and phone bills. Claiming 100% of your bill is almost always incorrect.

4. Mixing Travel and Holidays

Trying to deduct personal holiday costs by adding a small work-related activity doesn’t pass the ATO test. Only the work-related portion is claimable.

5. Forgetting Side Hustle Income

Income from rideshare driving, online selling, or freelance work must be declared. The ATO matches data from banks and platforms to tax returns, so omissions are quickly detected.

6. Ignoring Capital Gains on Assets

Selling property, shares, or cryptocurrency often attracts capital gains tax. Many taxpayers overlook this, only to face penalties later.

For Business Owners

Business owners face a different set of risks. Mistakes here can quickly snowball into large tax debts and compliance problems.

1. GST Misreporting

Claiming GST credits on purchases that don’t include GST, or forgetting to report GST on income, can lead to significant ATO adjustments and penalties.

2. Poor Record-Keeping

Bank statements alone aren’t enough. The ATO requires invoices and receipts to substantiate claims. Without them, deductions can be denied.

3. Employee vs Contractor Errors

Misclassifying workers can result in unpaid superannuation, payroll tax, and penalties. It’s one of the most common traps for small businesses.

4. Inaccurate Depreciation

Assets must be depreciated according to ATO rules. Failing to update depreciation schedules or applying incorrect methods can distort taxable income.

5. Claiming Private Costs Through the Business

Putting personal expenses like family holidays or home renovations through the business account may seem convenient, but the ATO will reject them and may apply penalties.

6. Late BAS or PAYG Lodgements

Missing due dates attracts penalties and interest. Repeated late lodgements can also put a business on the ATO’s radar for further scrutiny.

The Real Price of Getting It Wrong

Tax mistakes can be costly in more ways than one:

  • Financial penalties – The ATO may apply interest and fines on top of additional tax owed.
  • Missed opportunities – Wrong claims often mean missing legitimate deductions.
  • Audit stress – Once flagged, your affairs may be scrutinised for years.
  • Reputation damage – For businesses, mistakes can erode client and stakeholder trust.

Even honest mistakes don’t excuse incorrect returns. The onus is on the taxpayer to ensure claims are accurate.

How to Avoid Costly Mistakes

The good news is that avoiding mistakes is straightforward with the right approach:

  • Keep accurate records – Store receipts, invoices, and logbooks.
  • Use technology – Cloud accounting and receipt apps make compliance easier.
  • Stay updated – Tax law changes regularly; what was valid last year may not be today.
  • Ask before you claim – If in doubt, seek advice before submitting.
  • Engage a registered tax agent – Professional oversight ensures your return is both maximised and compliant.

FAQs About Tax Mistakes

What happens if I make a mistake on my tax return?

You can amend most returns online. If the ATO finds the mistake first, they may apply penalties or interest.

How far back can the ATO audit me?

Generally up to two years for individuals and four years for businesses, but there’s no limit if fraud or evasion is suspected.

Can I amend a return if I forgot a deduction?

Yes. You can lodge an amendment to include missed deductions or correct mistakes.

Are all donations deductible?

Only donations made to registered deductible gift recipients (DGRs) qualify. Receipts are required.

Can I claim personal expenses if I sometimes use them for work?

Yes, but only the work-related portion. For example, if you use your phone 30% for work, you can only claim 30% of the bill.

Final Word: Don’t Let Mistakes Cost You

The stray cat case may be extreme, but it shows how quickly a good intention can become a costly tax mistake. More often, errors come from over-claiming, misunderstanding, or missing income and deductions.

The cost of getting it wrong isn’t just denied deductions — it’s penalties, audits, and stress.

With the right advice, you can get it right the first time.

Speak to your RJS accountant today to make sure your next tax return is accurate, compliant, and audit-proof.

This article is published by R J Sanderson and Associates Pty Ltd ABN 71 060 299 783. This article contains general information only and is not intended to represent specific personal advice (Accounting, taxation, financial or credit). No individual personal circumstances have been taken into consideration for the preparation of this material. It is recommended that you obtain your own personal professional advice before making any financial or business decision.

R J Sanderson & Associates Pty Ltd
Last modifed
September 17, 2025

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