Most tax return problems come down to a small set of avoidable mistakes. Steer clear of these and your 2026 return will be smoother, more accurate, and far less likely to attract ATO attention. Below are the ones we see most often in practice, with simple steps to avoid each.
Leaving out income
Forgetting bank interest, dividends, a side hustle or a managed-fund distribution is one of the most common errors we come across. The catch is that the ATO already receives much of this information directly from banks, employers, share registries and platforms. When your return does not match their pre-fill data, it stands out quickly.
The fix is straightforward: declare everything, even small amounts. Common income people overlook includes:
- Interest on every bank account, including joint and offset accounts
- Dividends and managed-fund or ETF distributions
- Income from a second job, casual work or freelancing
- Money from gig platforms, rideshare, deliveries or online selling done as a business
- Capital gains from selling shares, crypto or an investment property
Over-claiming deductions
Claiming expenses you are not entitled to, or guessing amounts without records, can lead to an ATO adjustment, interest and penalties. The general rule is simple: you can only claim a deduction for a genuine expense you paid yourself, that directly relates to earning your income, and that you have not been reimbursed for.
Be especially careful with mixed-use costs like your phone, internet or car, where only the work-related portion is claimable. Claim the deductions you are entitled to, but keep them honest and supportable. If a figure is a guess, it is a risk.
Poor record-keeping
You can only claim what you can prove. Missing receipts, no logbook and vague estimates turn legitimate claims into shaky ones, and the ATO can disallow a deduction simply because you cannot substantiate it.
A little admin through the year fixes this entirely. A few habits that help:
- Keep digital copies of receipts, invoices and statements as you go
- If you claim a car, choose a method and keep the records to match. For 2025-26 you can use 88c per kilometre up to 5,000 km, or keep a logbook for actual expenses
- For home office costs, the fixed rate of 70c per hour for 2025-26 requires a record of the hours you actually worked from home
- Hold on to records for the period the ATO requires, generally several years after lodging
Getting work-from-home claims wrong
Working-from-home deductions are a frequent source of errors. The fixed-rate method of 70c per hour for 2025-26 is convenient, but it covers things like electricity, internet, phone and stationery, so you cannot then claim those same costs separately on top.
The alternative is the actual-cost method, which can produce a larger claim but demands detailed records and apportionment. Whichever you choose, the key is consistency between the method and the evidence you keep. Pick one approach and make sure your records support it.
Forgetting about interest, super and timing
A few changes are worth keeping on your radar. From 1 July 2025, ATO interest charges (the general interest charge and shortfall interest charge) are no longer deductible, so letting a tax debt run is now more expensive than it used to be.
On the upside, personal concessional super contributions can be a genuine deduction. The concessional cap is $30,000 for 2025-26 and contributions are generally taxed at 15% in the fund. If your total super balance is under $500,000, you may also be able to use carry-forward unused cap amounts from earlier years. The rules have conditions, so it is worth checking your position before contributing.
Lodging in a rush
Returns thrown together at the deadline are where mistakes creep in. Rushing means forgotten income, missed deductions and simple typos that can hold up your assessment or trigger a review.
Lodging early, with everything gathered, gives you time to get it right and to claim the deductions you are genuinely entitled to. It also helps to wait until your pre-fill data has landed, usually a few weeks into the new financial year, so you are not amending later. A calm, organised return is almost always a more accurate one.
How we can help
If you would rather have a registered tax agent handle the detail, that is exactly what we do. We check your income against ATO data, review your deductions for what is genuinely claimable, and make sure your records back it all up before we lodge.
Book a chat at nebulaaccounting.au or call 0433 822 227.
This article is general information only and does not take account of your personal circumstances — it is not personal tax, financial or legal advice. Tax laws change and apply differently to different people. Nebula Accounting Pty Ltd is a registered tax agent (No. 26259377); please speak with us or check with the ATO before acting.