How far back can you amend a tax return in Australia?

The answer depends on who you are and when your assessment issued, not on the financial year or the day you lodged. For most individuals the amendment period is two years from the date the ATO issued the notice of assessment. For sole traders and small business it is four years from the 2024-25 income year.

That start date matters. A return lodged in August and assessed a couple of weeks later is amendable until roughly the same time two years on. Lodge late and the clock starts late. The date is printed on the notice itself and shown in your ATO online account under your lodgement history, so it takes a minute to check where each year sits.

Once the period closes, the return generally cannot be amended and an overpayment stays with the ATO. There are limited circumstances where a longer period applies and the ATO can extend the period in some situations, but they are the exception. A registered tax agent will confirm where your return sits before anything else happens.

Why the date on the notice is the one that counts

People often assume the window runs from 30 June or from the date they lodged. It runs from the date the ATO issued the assessment, which is usually a short time after lodgement but can be longer. If you lodged several years through an agent at once, each year has its own assessment date and its own window.

Sole traders and small business

The longer period reflects the wider range of claims involved. Home office, vehicle, equipment, insurance, subscriptions and the cost of running the business all come into a review and the chance that something was missed is higher when the return was done in a hurry at the end of a busy year.

What to do if you are near the edge

If a year is close to closing, say so when you enquire. Reviews are handled in order, but knowing that a deadline is near lets the tax agent confirm the date first and tell you straight away whether there is time to act. Nothing is lodged without your written approval and the review itself is free.

General information only. It does not take account of your circumstances and is not tax advice. Untax is a marketing and referral service and is not a registered tax agent.