Default assessments: the ATO decided what you owe — without your return
In plain English
If returns or BAS stay unlodged, the ATO can issue a default assessment — its own estimate of what you owe, built from bank data, employer reports and industry benchmarks. Estimates skew high, and a default assessment usually brings a 75% administrative penalty on top of the tax. The debt is legally due even though you never lodged. The usual fix is not arguing in the abstract — it's lodging the real returns, backed by an objection where needed, inside the objection window.
Objection windows are running
You can object to a default assessment, but only within the statutory window — generally 2 years from the assessment for most individuals and small businesses (4 years for other taxpayers, and 4 years for GST assessments), and 60 days for the penalty notice. Late objections need a formal extension request the ATO doesn't have to grant. Meanwhile the debt is due and collectable — objecting doesn't pause recovery or the interest clock.
How default assessments work
Lodgment is the deal at the heart of self-assessment: you tell the ATO your numbers. When you stop lodging, the law lets the Commissioner make the numbers up for you — a default assessment of your income tax, or of GST and other amounts on unlodged activity statements. In building the figure, the ATO uses whatever it can see:
- your previously lodged returns and activity statements, uplifted for growth
- income data reported by employers, banks, government agencies and platforms
- small business benchmarks and industry statistics for your trade
You'll normally get a warning letter first, giving you a final chance to lodge before the assessment issues. (The ATO can skip the warning where it suspects assets are being moved or someone is about to leave the country.) Once issued, a default assessment is a real, legally due debt — enforceable by garnishee and everything else in the recovery toolkit, exactly as if you'd self-assessed it.
Why the number is usually inflated
Default assessments are deliberately conservative — against you. The data the ATO holds is mostly income data; it has your gross deposits and reported receipts but not your deductions, cost of sales, GST credits or losses. Benchmarks assume you performed at industry-typical margins in years where you may have barely traded. The practical result: default assessments routinely land far above what a properly prepared return would show. That's partly incentive design — the ATO would rather you lodge the real thing — and partly the burden of proof: once assessed, it's on you to prove not only that the assessment is excessive, but what the correct figure actually is. Silence concedes the inflated number.
The 75% penalty on top
A default assessment usually arrives with an administrative penalty of 75% of the tax-related liability — the price of forcing the Commissioner to assess you. That can rise to 90% for repeat cases, and failure-to-lodge penalties and general interest charge stack on separately (GIC is 11.43% p.a. for July–September 2026, and interest accrued from 1 July 2025 is no longer tax-deductible). The penalty is itself contestable: it can be objected to, and the ATO has discretion to remit it in whole or part — voluntary lodgment and cooperation are the classic grounds. See penalty remission.
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Why lodging real returns usually beats objecting alone
You have formal objection rights, and sometimes you need them. But an objection that just argues "the estimate is too high" goes nowhere — you must prove the correct position, and the only convincing way to do that is to prepare the actual returns from actual records. Which is why the standard playbook is:
- Reconstruct the records and prepare the true returns for every outstanding period — bank statements, invoices, payroll, loan accounts. Imperfect records can still support a defensible return.
- Lodge them, paired with an objection where required. Depending on the tax and timing, the real figures go in via lodgment, amendment or a formal objection with the returns as evidence — a registered tax agent will pick the right mechanism. The point is the ATO ends up assessing your evidence-backed numbers instead of its benchmarks.
- Ask for penalty and interest remission in the same breath — coming forward voluntarily and fixing lodgment is exactly what remission discretion exists for.
- Deal with the residual debt honestly. Whatever survives on the real numbers is a normal tax debt — payable, or manageable through a payment plan, or, if it's genuinely beyond you, a can't-pay conversation.
Formal disputes remain available when the ATO won't accept your figures — the machinery is covered in disputing an ATO debt. But remember the golden rule of tax disputes: the debt stays due and collectable while you argue. An objection is not a payment pause.
Companies: the estimates-and-DPN trap
For companies with unlodged BAS, default assessments have a nastier cousin: the ATO can raise estimates of PAYG withholding, GST and super and issue directors a director penalty notice on the estimated amounts. Because the underlying lodgments were late or never made, those penalties are typically lockdown — payment is the only way out, and disputing the estimate doesn't stop the 21-day clock. If a company has unlodged BAS and no notice yet, lodging now — even without paying — is usually the single most valuable protective step a director can take, because it preserves non-lockdown status and replaces inflated estimates with real figures.
WHAT THE ATO PAGE DOESN'T TELL YOU
A default assessment is often a door closing, not just a bill. It signals your file has moved from "lodgment reminder" to active enforcement — the same posture that produces garnishees, credit disclosure and, for old personal debts, offsets when historic debts resurface. The cheapest moment to fix a lodgment gap is before the ATO fills it for you; the second cheapest is immediately after.
Frequently asked questions
Is a default assessment legally enforceable if I never lodged anything?
Yes. Once issued it's a valid assessment and the amount is legally due — the ATO can collect it by garnishee, offset and court action like any other tax debt. Not lodging doesn't protect you; it's what triggered the assessment.
How long do I have to object to a default assessment?
Generally 2 years from the assessment for most individuals and small businesses, 4 years for other taxpayers, and 4 years (and one day) for GST assessments. Objections to the 75% penalty must be lodged within 60 days of the penalty notice (or by the deadline for the related assessment, if later). Out of time, you can request an extension — but the ATO doesn't have to grant it.
If I lodge my real return, does the default assessment just go away?
Not automatically — but lodging the true returns is the evidence that gets the assessment amended or an objection allowed, and in practice the ATO generally reassesses on properly supported real figures. The mechanism (lodgment, amendment or objection) depends on the tax and timing, which is where an agent earns their fee.
Can the 75% penalty be reduced?
Often, yes. The penalty can be objected to, and the ATO has a broad remission discretion — voluntary lodgment, cooperation, and circumstances explaining the lodgment failure all count in your favour. It rises to 90% for repeat non-lodgers, so the pattern matters too.
Do I have to pay while I dispute the assessment?
The due date generally stands while you object — interest keeps running and the ATO can pursue recovery. In practice the ATO often holds firmer action while a genuine objection with real evidence is on foot, but that's discretion, not a right. A payment plan alongside the objection is the usual protection.
Why did my company's directors get DPNs based on estimated debts?
Where BAS or SGC statements are unlodged, the ATO can estimate the liabilities and issue director penalty notices on the estimates — and because the lodgments were late, those penalties are usually lockdown, meaning only payment clears them. Lodging real figures promptly is the main protection.
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