Privately educating a Canberra child born in 2015 from preschool to year 12 is expected to cost $421,418, according to the Australian Scholarships Group's Planning for Education Index.

The survey has placed Canberra third behind Sydney at $541,275 and Melbourne at $502,088, and just below a projected national average of $456,933.

Sending a child through the territory's government school system is expected to be almost eight times cheaper at $53,564.

Meanwhile, the capital is set to be the cheapest metropolitan area to send a child through the systemic or religious school system at $207,732, below a national metropolitan average of $228,120.

Australian Scholarships Group chief executive John Velegrinis said although increasing education costs were not surprising, they were an incentive for parents to invest in their child's education early.

"The cost of education is only growing," he said.

"Over the last 10 years ... costs have been rising at twice the national headline rate of inflation.

"Quite often parents rock back in their seats and say, 'oh my lord'. Whatever you do or whoever you do it with, you've got to start planning early."

The index is based on a survey of ASG members, looking at the varying costs of educating a child starting kindergarten or early childhood education in 2019 and completing year 12 in 2032.

"What we asked parents for is a true estimate of the cost of education," Mr Velegrinis said.

"Everyone can look at school fees – you get a really simple response. When you factor in all the other items, such as transport costs, the cost of books, tablets, computers, uniforms, excursions, then you start to understand the true cost of an education."

Australian Education Union ACT secretary Glenn Fowler said the extra money spent on a private education was a "poor investment".

"Why would anyone want to add extra costs by paying for a private education?" he said.

"There's been a number of studies internationally and nationally over the last 12 months which make it very clear, taking into account socio-economic status, that the academic performance of children in public schools is at least as good as children at private schools.

"What I would say to parents is save the dough and take your kids to Disneyland."

Mr Fowler said some parents might associate non-academic opportunities with a higher price tag, encouraged by "an aggressive private school marketing campaign".

He was not surprised by the jump in fees by 2032.

"We have some of the finest public schools in the country that provide incredibly good opportunities for all comers, for all kids and all families," he said.

"There's great diversity, great inclusion, great tolerance; all those benefits at a fraction of the cost.

"School fees will never go down; they'll continue to rise."

Association of Independent Schools of the ACT executive director Andrew Wrigley said costs always factored into decisions around education but were not the first or only consideration when choosing a school.

"Schools have to be able to operate – fees are a major part of that, government funding is a small part of that," he said.

"Parents' choices about independent school education are usually based not only on what the cost is but whether the school is the best fit for their child.

"The end point is, can we afford it? Parents are investing in their kids' education."

Mr Wrigley said it was difficult to draw conclusions from the projected cost of religious education due to the variety of schools within the category.

He hoped parents made an active decision when choosing where to school their children.

"I hope every parent is making an actual choice about where their children go to school, whether it be a government school or a non-government school," he said.