For as long as most practitioners can remember, the interest the ATO charged on an unpaid tax debt was at least softened by being tax deductible. That quietly ended on 1 July 2025. General interest charge and shortfall interest charge incurred on or after that date are no longer deductible, and the change applies regardless of which income year the underlying debt relates to. It sounds like a technical footnote, but it materially changes the economics of carrying a tax debt, and it turns what many clients have treated as a flexible line of credit into one of the more expensive forms of finance available. For firms, it is one of the more useful conversations to have with clients this year, because the cost of doing nothing has gone up.
What actually changed, and the date that governs it
Two charges are affected. General interest charge (GIC) applies when a tax or super liability is not paid by its due date, compounds daily, and sits at a rate the ATO resets quarterly. Shortfall interest charge (SIC) applies where an amended assessment reveals that too little tax was paid, and is generally lower than GIC. Historically both reduced the real cost of a tax debt because they were deductible, effectively cutting the after-tax cost of the interest by the client's tax rate. From 1 July 2025 that deduction is gone for any GIC or SIC incurred on or after that date. The trigger is the date the charge is incurred, not the date it is paid and not the year the debt relates to, so interest on a genuinely old liability is still non-deductible if it accrues now. Charges incurred before 1 July 2025 remain deductible in the 2024-25 and earlier years, and there is a corresponding change on the other side: because the charges are no longer deductible, any GIC or SIC incurred from 1 July 2025 that the ATO later remits does not have to be included as assessable income.
The practical effect is a step-change in cost. With the deduction removed, a client now bears the full economic weight of a daily-compounding charge with no tax offset against it, which for many businesses pushes the effective cost of an ATO payment plan above what a commercial lender would charge. What used to be a manageable cash-flow timing tool has become one of the most expensive ways to fund a business, and the change is easy to miss precisely because the ATO debt itself looks the same on the statement. Only the after-tax maths has moved.
Why this reshapes the advice firms give on tax debt
The most immediate implication is that leaning on an ATO payment plan as cheap working capital no longer works. Where a client has an unavoidable debt, the plan should now be structured over the shortest timeframe the client can manage, because every extra month of a non-deductible, daily-compounding charge is pure cost with no offset. Paying the debt down faster, or clearing it outright where cash flow allows, is now more valuable than it used to be. There is also a refinancing angle worth raising carefully: interest on a commercial loan used to pay a business tax debt can still be deductible where the borrowing is genuinely connected to the business activity, which for some clients makes refinancing an ATO balance into a business facility both cheaper on rate and better on deductibility. That analysis needs care, because whether the interest is deductible depends on the character of the underlying debt and the entity involved, so it is advice to give deliberately rather than a blanket recommendation.
Remission remains the other lever. The ATO can still remit GIC and SIC where there are reasonable grounds, and early, genuine engagement improves the odds, though practitioners have noted the ATO's exercise of that discretion has tightened. The through-line for clients is that this change rewards paying on time and self-assessing accurately, because GIC is avoided entirely by paying by the due date and SIC is avoided by getting the return right the first time. The cheapest response to the new rule is simply not to incur the charge.
What firms should be doing about it now
This is a proactive-advice moment rather than a compliance task, and the firms handling it well are surfacing it with clients before the debt builds rather than after. Three habits do most of the work. First, encourage clients to set money aside for GST, PAYG withholding and super as it accrues, so the funds exist when the liability falls due and GIC never starts. Second, review any client sitting on an existing ATO payment plan, because the arrangement that made sense while the interest was deductible may now be worth compressing or refinancing. Third, treat accuracy at lodgement as a cost-saving measure in its own right, since an avoided amended assessment is an avoided shortfall interest charge. None of this is complicated, but it is the kind of advice that is easy to leave unsaid until a client notices their tax debt is costing more than they expected. Raising it first is exactly the sort of forward-looking guidance that separates a firm that files returns from one that manages a client's position.
