Does my child support automatically update when the other parent's income changes?

Only at specific trigger points. Services Australia uses the most recent ATO assessment for each parent, so it updates when the ATO has a newer figure (typically each year after tax lodgement). It also updates when either parent supplies a current-year income estimate. Outside those, the assessment stays at the existing figure until the next child support period starts (annually).

My ex got a big pay rise — do I need to do anything to get more child support?

Not immediately, but you can speed it up. The pay rise will flow through automatically once they lodge their tax return for the relevant FY (and Services Australia syncs with the ATO — usually within weeks). If you want it reflected sooner, you can ask Services Australia to use a current-year estimate based on payslips — your ex can supply one, or you can apply for a Change of Assessment under Reason 8 (earning capacity) if you believe their declared income materially understates reality.

My ex says they've lost their job. What happens to the assessment?

They can provide a current-year income estimate to Services Australia reflecting the reduced income. If accepted, the assessment is recalculated downward for the rest of the period. If you have reason to believe they're not really earning less (e.g. they've moved to cash work, started a business that's not yet declaring, or reduced hours voluntarily), you can apply for a Change of Assessment under Reason 8 (earning capacity) — the formula uses what they COULD reasonably earn, not what they declare.

What's Reason 8 (earning capacity) and when should I use it?

Reason 8 is one of the 10 Change of Assessment grounds — it asks Services Australia to use a higher figure than what's declared because the parent's actual earning capacity exceeds their declared income. It's the right tool when you suspect deliberate income suppression (a doctor who suddenly works part-time after separation, a tradie now paid in cash, a business owner whose declared salary halved while the business kept turning over). Services Australia weighs work history, qualifications, recent hours, and whether the reduction was reasonable. It's a high bar — personal choice to work less is generally accepted unless the reduction looks designed to reduce CS.

How long do current-year income estimates last?

Until the end of the current FY (June 30) or until reconciled when the actual tax return is lodged — whichever comes first. If the actual income at reconciliation is higher than the estimate, the underpayment is recovered (a CS debt). If it's lower, the overpayment may be recoverable depending on whether the estimate was reasonable. So providing an estimate that turns out to be too low creates back-payment exposure for the paying parent.

My ex won't tell me what they earn. How do I know if the figure on the notice is right?

You don't — Services Australia is the only party legally entitled to see both incomes. The notice shows each parent only their OWN ATI plus a "child support income" derived figure for the other parent. If the calculated outcome looks wrong (e.g. the payable amount is suspiciously low for what you remember your ex earning), the right move is a Change of Assessment application — Services Australia can compel disclosure of income, tax returns, and bank records as part of the review.

What happens when the other parent's income changes — child support

The other parent got a pay rise, lost their job, started a business, or stopped working. Here's when your child support assessment automatically updates, when it doesn't, and what to do if you suspect their declared income is wrong.

Income changes are the single most common trigger for child support disputes — your ex got a pay rise and you want more support, or they lost their job and now want to pay less, or they "started a business" and suddenly the formula spits out a much lower number. The system has rules for each scenario, but the rules differ depending on whether the change is automatic (driven by the ATO sync) or claimed (driven by an income estimate or earning-capacity argument).

This guide walks through what happens in each scenario.

The annual cycle — how income updates normally flow

Services Australia uses adjusted taxable income (ATI) for both parents — the same figure used in Centrelink and FTB. For most parents, that figure comes from the most recent ATO assessment.

The annual cycle:

You and your ex both lodge tax returns (between July and October-ish each year).
The ATO assesses each return.
Services Australia syncs with the ATO. Usually within weeks of assessment, sometimes longer.
The next child support period begins with the updated ATI for each parent.

So a pay rise your ex got in March 2026 typically flows into the formula around late 2026 or early 2027 — once they've lodged FY26 and the ATO has assessed. The lag is usually 6–12 months end-to-end.

When the cycle isn't fast enough — current-year estimates

If a parent's income has changed materially (typically 15%+ up or down) and they don't want to wait for the next annual cycle, either parent can supply a current-year income estimate. This tells Services Australia "use this figure instead of the ATO one for the rest of the FY".

Estimates are common in three scenarios:

Big pay rise / promotion / new job — paying parent's income went up significantly, receiving parent wants the formula to reflect it sooner.
Job loss / reduced hours — paying parent's income dropped, they want the formula to come down quickly.
Starting a business / sole trader — moving from PAYG to ABN, where the prior year's ATI is no longer a useful guide.

The estimate is provisional — at the end of the FY, when the actual tax return is lodged, Services Australia reconciles the actual income against the estimate:

If actual > estimate → the paying parent owes more, retrospectively, and a debt is raised
If actual < estimate (i.e. they over-paid) → recovery depends on whether the original estimate was reasonable

This is why estimating too low is dangerous for paying parents — a year of "I think I'll earn $60k" that turns out to be $80k creates a 12-month back-debt with penalty interest applied.

When you suspect the declared income is wrong — Reason 8

The hardest scenario is the one where you think your ex is deliberately understating their income — moved to cash work, started a business that's not really losing money, dropped to part-time "for personal reasons" right after separation.

The right tool here is a Change of Assessment under Reason 8 — "the parent's earning capacity exceeds their declared income".

Services Australia weighs:

Work history — what they earned before separation, what they're qualified to earn
Qualifications and skills — a paediatric nurse who's "now working at a cafe" has a clear earning gap
Hours worked — voluntary reduction to part-time without reason
Whether the reduction looks designed to reduce CS — timing relative to separation, communications, sudden lifestyle changes

The bar is high. Personal choice to work less is generally respected — Services Australia won't force a parent back into a high-paying job they don't want. But where the reduction looks deliberate, sudden, and aligned with separation, Reason 8 succeeds reasonably often.

The application process is the standard Change of Assessment process: 10 grounds, evidence-led, decision within 90 days, appealable to the AAT. See Change of Assessment guide for the full process.

Self-employed and business income — the special case

When your ex is self-employed or runs a company, the income picture gets murky. The notice will show their declared business income, but business income is much easier to manipulate than PAYG income:

Salary the owner pays themselves
Retained earnings the company keeps
Personal expenses run through the business
Loans from the company to the owner

For these cases, the relevant guide is Child Support for self-employed parents — it covers how the formula treats business structures and the audit triggers Services Australia uses. Reason 7 (financial resources) is more relevant than Reason 8 for owner-operated businesses, because the question isn't "could they earn more in a job" — it's "do they have substantial financial resources the formula isn't capturing".

Practical playbook by scenario

Scenario 1: Ex got a major promotion

Wait for the annual cycle if the next CS period starts within a few months.
If it's a long wait, ask your ex to submit a current-year estimate. They have an incentive to keep the relationship cooperative — but no legal duty.
If they refuse, Change of Assessment under Reason 8 isn't quite right (their declared income IS their earning capacity once it lands at ATO). The cleanest path is just to wait for the cycle.

Scenario 2: Ex says they lost their job

They submit a current-year estimate. Services Australia accepts it (subject to evidence — termination letter, payslips, Centrelink record).
The assessment recalculates downward.
You watch the reconciliation. If the actual income at reconciliation is higher than the estimate, you'll see backdated CS owed to you (or at least the assessment corrected).
If you suspect they're working cash-in-hand or have undisclosed income, Reason 8 / Reason 7 Change of Assessment is the path.

Scenario 3: Ex started a business and the assessment dropped sharply

Read Child Support for self-employed parents carefully — the formula treatment of business income is its own topic.
The right Change of Assessment ground here is usually Reason 7 (financial resources) rather than Reason 8 (earning capacity).
Gather evidence: ASIC company extracts, prior PAYG history, lifestyle indicators (new car, holidays, mortgage), bank statements if accessible through the Change of Assessment process.
The process is slower and harder than PAYG cases but Services Australia has compulsion powers — it can demand business records as part of the review.

Scenario 4: You're the paying parent and YOUR income changed

If your income went up, you can supply a current-year estimate or wait for the cycle. Wait is fine if your ex won't be massively disadvantaged.

If your income went down, supply a current-year estimate as soon as the change is real and documented. Don't wait — every fortnight that passes is CS being assessed at the higher figure, and the formula doesn't backdate downward easily. Estimate conservatively (slightly higher than your expected actual) to avoid reconciliation surprises.

How NestWise helps

The CS Assessment Scanner (scan a notice) keeps a record of each notice you receive, so when a new one arrives we compare the assessed ATIs against the previous notice and flag material changes — e.g. "Your ex's assessed ATI is 22% lower than the prior notice — this might warrant a closer look at whether they've supplied a current-year estimate, and whether the figure is reasonable."

The "Your CS picture" page (see CS picture) pulls together your most recent assessment with year-to-date NAP and other expense evidence — useful baseline if you need to consider a Change of Assessment.

Scan your latest assessment notice →