How Is Child Support Calculated? The 8-Step Formula (2026 Rates)

Services Australia calculates child support with an 8-step formula that combines both parents' incomes and their share of care nights. For child support periods starting in 2026, each parent first has a self-support amount of $31,046 deducted from their adjusted taxable income — that's one third of annualised Male Total Average Weekly Earnings (MTAWE), which is $93,137 for 2026. What's left is split into income percentages, offset against each parent's care percentage, and applied to a published "Costs of the Children" table. Sources: Services Australia basic child support formula page and child support basic values (operational guide 277-03160000), both checked 21 July 2026.

You can run your own numbers through the same 8 steps — including the 2026 Costs of the Children tables and care rounding rules — with our free Child Support Calculator.

This is Formula 1, the standard formula where both parents are assessed and there's one child support case (most separated families):

1. Child support income — each parent's adjusted taxable income, minus the $31,046 self-support amount, minus any allowance for other dependent children living with them.
2. Combined income — add both parents' child support incomes together.
3. Income percentage — each parent's share of the combined income.
4. Care percentage — each parent's share of care nights across the year (below 50% rounds down to a whole percent, 50% or more rounds up).
5. Cost percentage — care converted to a share of the children's costs using the care and cost table below.
6. Child support percentage — income percentage minus cost percentage. A positive result means you pay; negative means you receive.
7. Costs of the children — looked up in the annual Costs of the Children table using the combined income, the number of children, and their ages.
8. Annual rate — the positive child support percentage multiplied by the costs of the children.

The logic in plain English: the formula works out what the children should cost, then asks whether your share of the money matches your share of the care. If you have 60% of the income but provide 20% of the care, you pay the gap.

Parent A earns $90,000, Parent B earns $50,000, they have two children aged 7 and 10, and the children stay with Parent A 96 nights a year (roughly every second weekend plus half the school holidays). Using the 2026 values:

Parent A pays Parent B about $9,500 a year. The Costs of the Children figure comes from the 2026 table for two children aged 0-12 with a combined income in the $46,569-$93,137 band. Try your own combination in the Child Support Calculator — it itemises every one of the 8 steps exactly like this table.

Care is counted in nights per year and converted to a cost percentage in fixed bands — and the bands create cliffs worth knowing about. One extra night a fortnight can move you from "regular care" to "shared care" and change your assessment materially. The 2026 care and cost table (Child Support (Assessment) Act, s 55C):

Two rounding rules matter: a care percentage below 50% rounds down to a whole percent and 50% or more rounds up (so the two parents always total 100%), and a parent with less than 14% care has a 0% cost percentage — they pay child support but it doesn't reduce for those nights.

Two floor rates stop assessments reaching $0. The minimum annual rate is $551 per case for 2026 — it applies when the formula produces less than that and the paying parent has less than regular care (under 14% of nights). The fixed annual rate is $1,825 per child (capped at three children) — it applies instead of the formula when the paying parent's income is very low (under $26,720, the 2026 Parenting Payment Single maximum basic amount) but they didn't receive an income support payment, a rule aimed at parents who minimise reported taxable income. Source: Services Australia fixed and minimum child support assessments, checked 21 July 2026.

Also built into the formula: costs of the children stop increasing once combined child support income passes $232,843 (2.5 × MTAWE) — beyond that, extra income doesn't raise the assessment.

The formula is the default, not the last word. Binding or limited child support agreements and court orders override it. Either parent can also apply for a change of assessment under one of 10 legislated special reasons — the common ones are high costs of spending time with the children, a child's special needs, and a parent's income, property or financial resources not being reflected in their taxable income.

One trap worth flagging in balancing season: if you pay based on an income estimate and underestimate, the shortfall becomes a child support debt once your actual income is known — the same mechanism that creates FTB and CCS debts at balancing. Child support you receive also feeds into the FTB Part A maintenance income test, so a change in child support usually changes your FTB too. Keep estimates current with Services Australia, and pressure-test your position with the Child Support Calculator and FTB Debt Checker.

How much child support will I pay on my salary?

There's no flat rate per dollar of salary — the formula depends on both parents' incomes and the care split. As a worked example with 2026 rates: a parent earning $90,000 with two children under 13, 96 nights of care a year, and an ex-partner earning $50,000 pays about $9,500 a year ($365.38 a fortnight). Change any input and the number moves; use the free Child Support Calculator for your own figures.

What income is used for child support?

Your adjusted taxable income for the last relevant financial year — taxable income plus add-backs such as reportable fringe benefits, salary-sacrificed super, and net investment losses. Each parent then has the 2026 self-support amount of $31,046 deducted before percentages are worked out.

Does 50/50 care mean no child support?

Not necessarily. Equal care equalises the cost percentages (50% each), but if one parent earns significantly more, their income percentage still exceeds their cost percentage and they pay the difference. With genuinely equal incomes and equal care, the assessment is $0.

What is the minimum child support payment in 2026?

The minimum annual rate is $551 per case for 2026, applying when the formula result is lower and the payer has less than 14% care. A separate fixed annual rate of $1,825 per child (up to 3 children) applies to low reported incomes without income support. Both figures are indexed each calendar year.