But the Australian Taxation Office expects the majority of outstanding returns to be lodged by registered tax agents over the coming months, with those who signed up with an agent before the deadline able to file returns as late as May 15 next year.

Data provided to the Sunday Canberra Times by the tax office shows 182,113 individual taxpayers in the ACT lodged their 2017-18 returns before October 31.

The figure represents about 87 per cent of the returns expected from ACT taxpayers.

Many Canberrans just snuck in before the deadline this year, with 24,831 lodging their tax returns between October 26 and 31.

The ACT ranked fifth among the states and territories in terms of taxpayers lodging on time. Tasmania led the way, with 99 per cent of those expected to lodge a return doing so before October 31, while NSW lagged behind all other jurisdictions with just 80 per cent beating the deadline.

Individuals who did not register with a tax agent or lodge their tax return before October 31 could face penalties of $210 for every 28 days their return is overdue, up to a maximum of $1050.

Australian Taxation Office assistant commissioner Kath Anderson said some of the main reasons people lodged returns late or not at all were because they didn't realise they needed to submit one, they were expecting a large debt, or they thought they would get a small refund and didn't consider it a priority.

Others ran out of time or had fallen behind in their lodgements, then put off lodging their most recent tax returns because they were worried about facing penalties.

Ms Anderson said more people were lodging their returns on time than in previous years, but the preliminary data on 2017-18 lodgements could still change.

"In the coming months the ATO will conduct a range of data-matching activities to identify those taxpayers who are not required to lodge, for example, those who earned less than the tax-free threshold, as well as those who are yet to lodge," Ms Anderson said.