Cost percentage
Cost percentage is the share of a child’s costs that the formula treats you as meeting through care. It is based on your care percentage but uses ranges rather than a one-to-one match.
Changes in care may not always affect your cost percentage, so the assessment can remain the same.
Definition
The cost percentage is used by the child support formula to determine how much of the costs of a child, a parent or non-parent carer is meeting through care.
A cost percentage is calculated for each child in an assessment because the care arrangement for each child must be recognised. The cost percentage is used to calculate the child support percentage.
The cost percentage is determined according to the person’s percentage of care for a child, using the cost percentage table.
Percentage of care — Cost percentage
0 to less than 14% — Nil
14% to less than 35% — 24%
35% to less than 48% — 25% plus 2% for each percentage point over 35%
48% to 52% — 50%
More than 52% to 65% — 51% plus 2% for each percentage point over 53%
More than 65% to 86% — 76%
More than 86% to 100% — 100%
Definition source: Guides to Social Policy Law, Child Support Guide, Version 4.97, released 20 March 2026, 1.1.C.200 Cost percentage.
Role in the formula
Cost percentage is the care-based credit in the formula. It represents the share of the child’s costs you are treated as meeting directly through care.
The formula compares each parent’s income percentage with their cost percentage. A positive result produces a payment. A negative result produces an entitlement.
Cost percentage follows care bands. Within a band, the value is fixed or moves within a defined range. Because of this structure, small changes in the care percentage can leave the same cost percentage in place.