Tax Return 2026: 5 Mistakes Costing Australians Thousands (myTax Guide)

By The Fine Print editorial team  |  Last updated: June 2026  |  11 min read  |  ⚠️ Not financial advice

Tax return season 2026 is here — and Australians are still losing thousands of dollars making the same avoidable mistakes. The ATO’s data-matching technology has never been more powerful, myTax makes lodging feel deceptively simple, and the combination is a recipe for rushed, expensive errors. Whether you’re over-claiming deductions you’re not entitled to or under-claiming ones you are, the cost is real. In April 2026, the ATO named its focus areas for 2025–26 individual returns — and if you’re making any of these five mistakes, you’re exactly who they’re looking for. ^[2]

What the ATO Is Targeting in 2026

In April 2026, the ATO publicly named its three focus areas for individual 2025–26 tax returns: work-related expenses (particularly WFH and car claims), unreported income (side gigs, cash jobs, investment income), and correct use of the new fixed-rate WFH method. ^[2] Assistant Commissioner Anita Challen warned Australians not to deliberately “pad” their deductions, stressing that data-matching systems will detect anomalies. ^[2]The ATO’s data-matching now pulls information from banks, employers, sharing-economy platforms, health funds and investment providers — often before you’ve even opened myTax. For 2026, ABC reports the ATO again urging taxpayers not to lodge on 1 July before income and interest data has flowed through, because rushed returns are about twice as likely to contain errors. ^[5][1]

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❌ Mistake 1: Treating Private Spending as “Work-Related”

The ATO says millions of Australians are incorrectly claiming private expenses as work-related deductions — including baby items, gym gear and everyday clothes that aren’t protective or occupation-specific. ^[1][7] ABC’s 2026 tax-time coverage reports the ATO warning that “chasing tax deductions” for private spending can lead to audits, penalties and interest charges — wiping out refunds and sometimes leaving taxpayers owing more than they ever expected to claim. ^[7][1]The problem is a double loss. If you claim a $500 private expense and get caught, you lose the deduction and face a penalty — often 25% of the tax shortfall, rising to 75% for deliberate avoidance. You still paid the original cost. You also distracted yourself from legitimate deductions you could have claimed properly. The risk-reward calculation is almost never in your favour. ^[2]

❌ Mistake 2: Over-Claiming WFH and Car Expenses

Working-from-home deductions are one of the ATO’s sharpest focus areas for 2026. The fixed-rate WFH method has been updated to 70 cents per hour, but it now requires stricter record-keeping: you must track total hours worked from home, phone and internet usage, and energy and running costs. Many people are still using old or made-up numbers — estimating hours months later, or claiming 100% of phone and internet without any evidence — and the ATO’s data-matching flags these patterns. ^[4][2]Car expenses are equally targeted. The cents-per-kilometre method is straightforward for up to 5,000 km per year, but the kilometres must be for work-related travel — not commuting (home to work), not personal errands. People claiming personal trips or commuting without logbooks or work-journey records are breaching the three golden rules, and the ATO knows it. ^[8][2]

💡 WFH: what you must record for the 70c/hour method

• A diary or calendar record of actual hours worked from home (not a rough estimate).
• Evidence of additional phone, internet and energy costs attributable to working from home.
• Records must be kept for the full income year — a sample period is no longer sufficient. ^[4]

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❌ Mistake 3: Forgetting Income (Especially Side Hustles)

The ATO is explicitly targeting unreported income in 2026 — including side gigs and freelance work, cash jobs, interest and dividends, and rental income (Airbnb and traditional). Their data-matching system pulls from banks, employers, sharing-economy platforms and investment providers. If you earned income and didn’t declare it, the ATO often already knows. ^[8][2]Under-reporting income can result in an amended assessment, penalties of up to 75% of the tax shortfall (for deliberate omission) plus interest charges, and in serious cases, prosecution. ^[2] For the growing number of Australians earning income through Uber, Airbnb, Airtasker, Etsy or freelancing platforms, this isn’t a theoretical risk — the ATO has direct data-sharing arrangements with many of these platforms.

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❌ Mistake 4: Poor Record-Keeping and “Guesstimate” Deductions

Tax professionals in 2026 consistently say most tax issues come from missing records, not bad intent — people genuinely believe they spent the money, but when the ATO asks for evidence, they can’t provide it. When that happens, the ATO can disallow the deduction entirely, even when the expense was real and legitimate. You lose the deduction and still paid the original cost — the worst of both worlds. ^[10][2]This matters most for WFH hours (estimated months later), car kilometres (no logbook), charitable donations (receipts lost), union fees (invoice not kept), and work equipment (no records of work-use percentage). The solution is not a different deduction strategy — it’s a record-keeping system that runs year-round, not just in July.

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❌ Mistake 5: Not Checking for Old Debts and Offsets

This is the mistake that blindsides people completely. In 2023, SBS revealed that the ATO had reactivated up to 290,000 “on-hold” debts totalling about $274 million. The ATO can automatically offset your tax refund against these old debts — and it says it has “very limited discretion” not to do so once the debts are active. ^[6]Taxpayers who don’t check their ATO Online account in advance can be shocked when a planned $2,000 refund disappears entirely — blowing up budgets for bills or planned expenses. The ATO defended the practice as legal and required, but the story highlighted how opaque communication leaves honest taxpayers completely blindsided. ^[6] ⚠️ Check before you lodge: log into myGov → ATO → “View account” and look for any existing debts, amended assessments or payment plans. Know what’s there before your refund hits — not after it disappears.

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✅ Three Actions to Take Right Now

Action 1: Set up myTax properly — and don’t rush

Before 30 June: log into myGov, make sure your ATO is linked, and check your account for existing debts. In July: wait until late July so most pre-fill data (income, interest, health funds) has loaded. Only lodge once you’ve checked every pre-filled item for accuracy and confirmed all your income sources. The ATO’s own data shows rushing in early July roughly doubles your chance of making a mistake. ^[5][3]

Action 2: Apply the three golden rules to every deduction

Before typing any dollar amount into myTax, ask: Did this directly help me earn my income? Did I pay for it (and not get reimbursed)? Do I have evidence — receipt, logbook, diary, hours record? If the answer to any of these is no, don’t claim it, or get advice first. The three golden rules are the ATO’s own framework, and they apply to every single deduction. ^[4][2]

Action 3: Create a year-round “ATO folder” so 2027 is painless

Set up a digital folder — in cloud storage or your phone — called “Tax 2025–26” with subfolders for work expenses, WFH, car, donations, investment and rental. Add a simple notes file or spreadsheet to log WFH hours and work trips as they happen. At year-end, this lets you maximise legitimate deductions and satisfy ATO substantiation rules without guesswork. ^[10][2]

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❓ Frequently Asked Questions

When is the 2026 tax return due?

31 October 2026 for self-lodgers via myTax. Registered tax agents on a lodgement program can get a later due date — sometimes extending to May 2027. If you’re unsure, contact an agent before 31 October. ^[3]

Can the ATO take my refund for an old debt?

Yes — automatically and with very limited discretion not to. Check your ATO Online account for any “on-hold” or active debts before you lodge. SBS reported in 2023 that up to 290,000 Australians had old debts reactivated, wiping their expected refunds. ^[6]

What are the ATO’s focus areas for 2025-26 returns?

Three areas named in April 2026: (1) work-related expenses, especially WFH and car claims; (2) unreported income — side gigs, cash jobs, investment income; (3) correct use of the 70c/hour fixed-rate WFH method and proper substantiation records. ^[2]

What’s the penalty for over-claiming deductions?

If the ATO disallows a deduction, you owe the additional tax plus interest. Penalties range from 25% of the shortfall (careless) to 75% (deliberate). You also lose the deduction even if the underlying expense was real. Don’t claim what you can’t prove. ^[2]

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⚖️ The Fine Print Verdict

The ATO’s systems have levelled up significantly. If you’re still lodging your tax return the same way you did in 2015 — rough WFH estimates, commuting kilometres as “work travel,” private expenses dressed up as deductions — you’re either overpaying tax or walking into an audit. The five mistakes above cost Australians real money every year. Most of them are avoidable with about 20 minutes of preparation and a basic record-keeping habit started right now.

👉 Log into your ATO Online account today. Check for debts. Set up your tax folder. Don’t lodge in a rush — and don’t tip Canberra money you’re not legally required to pay.

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📚 Sources & References

1. ABC News, “Tax time 2026: ATO warns millions of Aussies claiming tax deductions,” 2 June 2026. abc.net.au
2. Yahoo Finance / ATO, “ATO reveals focus areas for end-of-financial-year tax returns as workers warned over common claims,” April 2026. finance.yahoo.com
3. ATO, “Lodge your tax return online with myTax,” 2026. ato.gov.au
4. ATO, “Overview of key changes — Tax Time 2025–26,” 2026. ato.gov.au
5. ATO / WIN News Illawarra, “Aussies lodging tax returns promptly — ATO warns those who rush,” 2026. (Early-lodgement warning)
6. SBS News, “Are you one of almost 300,000? Why your tax refund might disappear this year,” 2023. sbs.com.au
7. ATO, “Latest news on tax law and policy,” 2026. ato.gov.au
8. Tax Agent in Perth, “10 common tax return mistakes to avoid in 2025 — ATO checklist,” 2025. taxagentinperth.com.au
9. Facebook / DMarge, “Australians warned ATO is identifying [discrepancies] faster,” 2026.
10. Zimsen Partners, “Tax returns 2026: common tax mistakes Australians make — expert interview,” 2026. zimsenpartners.com.au
11. GT Law, “Financial services regulatory recap — week commencing 2 March 2026,” 2026. gtlaw.com.au
12. Baker McKenzie, “Australia Budget bites: CGT discount and negative gearing,” May 2026. bakermckenzie.com

This article is general information only and does not constitute tax or financial advice. Tax rules change each year — always verify with the ATO (ato.gov.au) or a registered tax agent before lodging your return. The Fine Print 🇦🇺 is not affiliated with the ATO.