While Mr Barr would not comment ahead of the budget release, the latest forecasts released in February estimated an $11 million surplus in 2018-19, growing to a $79 million surplus by 2020-21.

Long a key political goal of Mr Barr's, a "balanced budget", would allow for small surpluses and small deficits in alternating years, depending on government spending and economic conditions.

If the budget makes good on the current estimates, it would be the first time in eight years the territory government's balance sheet has been in the black, though budget forecasts in 2016-17 and earlier, for surpluses in 2018-19, have not eventuated.

Despite those estimates, the $11 million position forecast in the mid-year update was an improvement on the $87 million deficit estimated for 2017-18 in last year's budget, a deficit that was reduced to $41 million by February this year, and the coffers have been creeping closer to the black since 2016-17.

But the latest boost was mainly due to updated population figures showing an extra 7000 people had made Canberra home in 2016 then previously forecast, leading to $45 million extra in Commonwealth grant payments, as well as an extra $20 milion-odd from ACT government land sales revenue.

But that "balanced budget" comes at a cost to many Canberrans, with a rising overall tax take, land sales revenue and rates helping to pay for the light rail project, among others, benefiting only a smaller portion of residents.

If the most recent estimates remain, total general rates revenue would rise 9.5 per cent from $487 million this year to $533 in 2018-19, land tax revenue will rise 8.4 per cent from $130 to $141 million.

For residential ratepayers, unit owners can expect another big rise - with a $115 average rise expected in 2018-19, not including the expiry of the one-off $100 "rebate" for changing the way unit rates were calculated last year.

In effect, it means unit owners, on average, would face an extra $365 a year on their rates bill, compared to 2015-16 figures, while the effect will be greater this year, as the $100 rebate expires from July, as the extra $115 kicks in.

Owners of detached homes can expect to face another seven per cent rate rise in 2018-19, after a similar rise last year and the nine per cent increase in 2015-16, while unit owners will join house owners with seven per cent average rises from 2019-20.

The government's 20-year tax reforms, centred on abolishing stamp duty, will also continue this year, which would save, on a $600,000-odd median Canberra house, about $1321 in stamp duty, in 2018-19 compared with last year.

Current forecasts also show a 6.5 per cent jump in motor vehicle registration revenue, and a 12 per cent rise in fire and emergency services levy revenue, likely partly due to population rises and another increase this year.

The government has already announced extra spending on mental health, the Calvary Bruce Public Hospital, some extra police, teacher training, emergency services equipment, electric vehicle charging stations roads and bicycle paths.

Affordable housing is expected to form a central plank in tomorrow's budget as the government draws up a new ACT strategy, while Canberra Theatre could also be in for some new funds ahead of a proposed revamp.