The biggest overhaul of the child support system for separated parents in more than two decades will come into effect on Tuesday.
The federal government says while a few parents will have to pay more in child support to former partners, most would not be greatly affected.
The most significant change is the way payments will be calculated for around 1.5 million separated and divorced parents nationwide.
The federal government says the new formula aims to share the costs of raising children more fairly and replaces a 20-year-old mathematical calculation.
It treats both parents incomes equally and takes into account the amount of care each parent provides.
Previously a parent had to give more than 30 per cent of care before there was a reduction in payment to the primary care giver.
The formula also treats the cost of raising children from first and second families equally.
It also takes into account additional incomes, such as pensions and salary sacrifice, when calculating payments.
Child Support Agency (CSA) acting general manager Trevor Sutton said only a small number of people would see significant changes in their payments.
"For the vast majority of people the changes won't be huge in terms of dollar losses or gains," Mr Sutton told AAP.
"But some parents will be upset and it is understandable, but our main message is for people to contact us and talk about the changes so we can properly explain them."
Human Services Minister Joe Ludwig said the new formula was based on the cost of raising children today.
"There have been considerable changes to Australian society since the Child Support Scheme was created 20 years ago," Senator Ludwig said in a statement.
Other changes to the system include measures to crack down on suspected child support cheats.
As of Tuesday, CSA will have the ability to employ private investigators to spy on suspected offenders.
The measure, announced by the federal government last week, is designed to help the CSA collect debts of $1 billion.
Senator Ludwig said the new scheme "aims to meet the best interests of children, reduce conflict between parents and ensure child support is paid in full and on time".
Parents can view detailed information about the new scheme on the CSA website www.csa.gov.au/schemereforms.