Deadlines and penalties
The tax calendar has one date that matters above all others: 31 October. That is the deadline for lodging your own return. Everything else — agent dates, penalties, interest — flows from whether you meet it.
| Date | What it is |
|---|---|
| 1 July | Lodgment opens for the year just ended |
| Late July | Most pre-fill data is in; wait for "Tax ready" |
| 31 October | Due date if you lodge your own return (myTax or paper) |
| 31 October | Last day to join a registered tax agent's client list for their later dates |
| 15 May (following year) | Later due date under a tax agent's lodgment program, if eligible |
When 31 October falls on a weekend
If 31 October falls on a weekend, the self-lodger deadline moves to the next business day. For the 2025–26 return, 31 October 2026 was a Saturday, so the deadline was Monday 2 November 2026. For the 2026–27 return, 31 October 2027 is a Sunday, so the deadline moves to Monday 1 November 2027. Note that the 31 October date for joining a tax agent's client list does not move — the ATO has confirmed agents must add new clients by 31 October itself.
Failure-to-lodge penalties
If your return is late, the ATO can apply a failure-to-lodge penalty of one penalty unit for each 28-day period (or part of one) that it is overdue, capped at five units. One penalty unit is $330 (for offences on or after 7 November 2024), so the maximum for a small entity is $1,650. Larger entities face higher multiples. The ATO does not always apply the penalty — a first-time short delay with a good history is often forgiven — but you cannot rely on that.
Interest on amounts owing
If you owe tax, general interest charge (GIC) applies to the unpaid amount after the due date shown on your notice of assessment. From 1 July 2025, GIC is no longer tax-deductible, which makes ATO debt materially more expensive than it used to be. If you cannot pay in full, contact the ATO before the due date — payment plans are available, and interest is generally still charged, but a plan stops the situation getting worse.
If you are already late
Lodge as soon as you can. The penalty grows with time, and lodging stops the clock. If several years are outstanding, lodge the oldest first or speak to a registered tax agent, who can bring you up to date and may be able to arrange lodgment under their program. The ATO can amend an assessment for up to four years after lodgment (longer for fraud or evasion), so keeping your records matters even after you have lodged.
Sources: Australian Taxation Office (ato.gov.au) — Lodgment dates; Failure to lodge on time penalty; Penalty units; Moneysmart (moneysmart.gov.au) — Lodging a tax return.