Every tax season there is a deadline that trips up small business owners more than any other, and it is not the one most people are thinking about. If you lodge your own tax return, without a registered tax agent, your 2025-26 return is due on 31 October. That date is five weeks away.

Who this actually applies to

If you are a sole trader or an individual preparing your own return, either on paper or through myTax, 31 October is your due date. It catches plenty of people out because the "everyone has until May" idea that circulates is only true for clients of a registered tax agent, and only under certain conditions.

The tax agent workaround, and its catch

If you engage a registered tax agent, your return can generally be lodged as late as 15 May 2027 under the ATO's lodgment program. But the catch matters: you need to be on that agent's client list, with any earlier outstanding returns already lodged, by 31 October. Signing up with an agent on 5 November does not retrieve the extension. The window to buy yourself the later date closes on the same day the self-lodge deadline falls.

What happens if you miss it

The failure to lodge on time penalty is calculated in blocks. It starts at $364 for a return that is even one day late, and another $364 is added for each following 28 day block the return stays outstanding, up to a cap of five blocks, or $1,820. The penalty applies automatically from the ATO's system, whether or not anyone has called you about it. The ATO can remit the penalty where there is a genuine reason and you lodge promptly once you do act, but that is a discretion, not a right.

A date worth noting

31 October 2026 falls on a Saturday this year. If you are self-lodging, treat that as a reason to get it done before the weekend rather than a reason to relax, since bank holidays and website load are not something you want to be testing at the last minute.

What to do this week

  • Sole traders with simple affairs: gather your income and expense records now and lodge through myTax well before 31 October.
  • Anyone who normally uses an agent but has not engaged one yet this year: call now. Being on the books before 31 October is what protects the May deadline.
  • Behind on a prior year return: get that lodged first. An outstanding earlier year can affect whether the later deadline applies to this year's return at all.

None of this is new law, it is simply a date that is easy to lose track of between BAS cycles and payday super. Five weeks out is exactly the right time to act on it.