The introduction of the fee means families of year 11 and 12 students starting at Radford in February will pay almost $2000 more than those who enrolled in 2017.

Including price increases on normal tuition, parents of newly-enrolled college students will pay $18,045 for 2018, compared to $16,130 the year before.

Fee schedules released by Canberra's independent schools show Radford is the ACT's third most expensive non-government school.

Canberra Grammar has retained the top title with families of year 12 students to fork out at least $23,830 for the new school year.

Canberra Girls Grammar asks $22,540, Marist College $11,286 and Burgmann Anglican School and St Edmund's College $10,800.

Brindabella Christian College follows on $9810, then Trinity Christian School ($9575), Daramalan College ($8940), Merici College ($8204) and St Francis Xavier College ($7771.98).

Each figure does not include fees for specific subjects or camps.

A letter sent to parents by Radford's board detailed "significant new factors" as driving its decision on making the levy compulsory, including the $23 million cut faced by the school over the next decade thanks to the federal government's new funding model.

Former chairman Ian Morison's letter also pointed to a decrease in the number of families making the formerly voluntary contribution, with fewer than 70 per cent coughing up what was a $1400 fee in recent years.

Mr Morison said because the building fee was compulsory it was no longer tax-deductible.

"After much deliberation, the board has determined to replace this voluntary building and maintenance fund donation (previously $1400 per child) with a lower, but compulsory, capital levy of $1190 per child commencing from 2018," he said.

"The levy is the fairest way of ensuring that all families contribute equally towards the continued improvement and development of the school facilities.

"This was a difficult decision, but was made in the best interests of the college and the families it serves."

Radford's redevelopment will allow for new junior school specialist classrooms, new years three and four classrooms, a new secondary school commons building and outdoor space, the ongoing refurbishment of secondary school classrooms and landscaping of the whole Bruce campus.

Tuition fees rose 4.3 per cent, according to Mr Morison.

Canberra's Catholic schools feared fee increases of up to $5000 when the government announced its new funding model, but fees have increased only modestly thanks to a government handout of about $40 million for 2018.

Catholic Education Office Archdiocese of Canberra and Goulburn director Ross Fox earlier this year said the transition funding allowed school fees to be maintained.

"Catholic education will work to keep fees affordable for parents but this will require long-term commitment to fair funding for students in non-government schools in Canberra," he said in October.

Further detail on transition funding was released recently.