Best Child Support Calculator (Australia)
We tested six popular online calculators for estimating child support in Australia, including the official government estimator. The calculators were compared for accuracy, scope, and ease of use based on three case scenarios.
Different calculators suit different purposes. ChildSupportCalculator.au ranked first overall, followed by Child Support Australia, and Services Australia.
The Services Australia estimator is the official benchmark for accuracy, but that does not make it the best tool for every use. Other calculators matched the official estimator while offering faster results, easier change testing, and even a greater range of cases that can be handled.
Calculator Ranking
The ranking gives most weight to accuracy and whether the calculator could reproduce the tested child support scenarios. Speed and ease of use were considered also. Testing was done on 1 June 2026.
Calculator labels: CSC.au = ChildSupportCalculator.au; CSA = Child Support Australia; Services = Services Australia; AusCS = AusChildSupport; Unified = Unified Lawyers; Custody X = Custody X Change.
| Rank | Calculator | Accuracy | Relevant child | Multi-case | Speed | Ease of use |
|---|---|---|---|---|---|---|
| 1 | CSC.au | Strong | Strong | Strong | Strong | Strong |
| 2 | CSA | Strong | Partial | Limited | Strong | Strong |
| 3 | Services | Strong | Strong | Limited | Limited | Limited |
| 4 | AusCS | Partial | Partial | Partial | Limited | Partial |
| 5 | Unified | Partial | Limited | Limited | Partial | Partial |
| 6 | Custody X | Limited | Limited | Limited | Strong | Strong |
Rating scale: Strong means the calculator performed well on that criterion. Partial means it worked with limitations, approximations, or extra steps. Limited means the calculator lacked required inputs, produced unreliable results, or was difficult to use for that criterion.
Scenario 1: Standard Formula Test
The first test used a standard child support scenario with no relevant dependent children and no multi-case child support arrangements. The case allowed each calculator to be tested on the main Australian child support formula without complications.
Scenario used for the test
The scenario involved two parents with taxable incomes of $120,000 and $100,000.
- Children: three children in the case, with two aged under 13 and one aged 13 to 17.
- Care pattern: Parent A had 160 nights of care per year.
- Common arrangement: 160 nights is a common arrangement, broadly reflecting a 6:8 fortnightly split with 8 weeks of school holidays divided evenly.
- Care percentage: 160 nights produced a raw care percentage of about 43.95%, which is rounded to 43% for child support.
We used the care percentage calculator to find the rounded care percentage. This rounded percentage comes from the legislated method used for Australian child support assessments.
Services Australia produced an annual child support estimate of $6,843. This was used as the benchmark result for the test.
| Calculator | Result | Test outcome |
|---|---|---|
| Services Australia | $6,843 per year | Official benchmark result. |
| Unified Lawyers | $7,737 per year | The exact rounded care percentage could not be entered. Care was entered as 6 nights out of 14. |
| Child Support Australia | $6,843 per year | Matched the Services Australia result. |
| Custody X Change | $430 per month, about $5,160 per year | Child ages could not be specified, so the scenario could not be reproduced fully. |
| AusChildSupport | $7,737.28 per year | Care had to be entered as 6 nights out of 14 rather than the rounded 43% care figure. |
| ChildSupportCalculator.au | $6,843 per year | Matched the Services Australia result. |
Services Australia produced the official benchmark result of $6,843 per year. This was treated as the reference point for assessing whether the other calculators reproduced the standard formula outcome.
Child Support Australia and ChildSupportCalculator.au also produced $6,843 per year. Both matched the Services Australia result for the standard formula test.
Unified Lawyers and AusChildSupport produced higher estimates. In both cases, the difference appears to come from the care input. The calculators required care to be entered as 6 nights out of 14, rather than allowing the formula-ready rounded care percentage of 43% to be used. Simple nights-per-fortnight input is often good enough for ordinary estimates, but it was not precise enough to reproduce this test scenario exactly.
Custody X Change produced a lower estimate. The main limitation was that the calculator did not allow the ages of the children to be specified. Australian child support calculations use different cost values for children aged under 13 and children aged 13 to 17, so it is unclear what formula the calculator applied.
Scenario 2: Relevant Dependent Child Test
The second test used the same base scenario, but added one relevant dependent child for Parent A. We compared how each calculator dealt with the income adjustment required when a parent has another dependent child in their household.
Scenario variation
The base case was unchanged from Scenario 1, with taxable incomes of $120,000 and $100,000.
- Children in the child support case: three children, with two aged under 13 and one aged 13 to 17.
- Care pattern: Parent A had 160 nights of care per year, rounded to 43% care for child support.
- Extra dependent child: Parent A also had one relevant dependent child aged under 13.
- Multi-case arrangements: none.
A relevant dependent child reduces the parent’s child support income before the final payment amount is calculated.
Services Australia produced an annual child support estimate of $4,491. This was used as the benchmark result for the second test.
| Calculator | Result | Test outcome |
|---|---|---|
| Services Australia | $4,491 per year | Benchmark result. |
| Unified Lawyers | No result | No option was found for adding a relevant dependent child. |
| Child Support Australia | $4,490 per year | Matched the benchmark within $1 after following its instructions for estimating the adjustment through the normal calculator. |
| Custody X Change | No result | No option was found for adding a relevant dependent child. |
| AusChildSupport | $5,308.52 per year | The relevant dependent child could be added directly, but care still had to be entered as 6 nights out of 14. |
| ChildSupportCalculator.au | $4,490 per year | Matched the benchmark within $1 after using its income adjustment calculator. |
Services Australia produced the benchmark result of $4,491 per year.
Child Support Australia produced $4,490 per year after following its written instructions for estimating the relevant dependent child adjustment through the normal calculator. The instructions are an extra feature below the calculator rather than a built-in input field. This is easy enough for users with strong basic numeracy, but less seamless than entering the extra child directly.
ChildSupportCalculator.au also produced $4,490 per year. It handled the relevant dependent child through a separate income adjustment calculator, which calculated the revised income figure to use for the parent with the dependent child. This added a separate step, but the final estimate matched the official result within rounding.
Unified Lawyers and Custody X Change could not reproduce this scenario because no option was found for adding a relevant dependent child. This is a functional limitation.
AusChildSupport provided the smoothest experience for entering the relevant dependent child. The extra child could be added directly in the step-wise process. However, the result remained higher than the benchmark. The likely explanation is the same care-entry issue observed in Scenario 1. Care had to be entered as 6 nights out of 14, rather than the rounded care percentage used in the official formula scenario.
Scenario 3: Multi-Case Allowance Test
The third test built on the previous scenario by adding a multi-case child support issue for Parent B. Parent B had another child support case involving one child aged under 13.
Scenario variation
The base case remained the same as Scenario 2, with Parent A having one relevant dependent child aged under 13.
- Additional case: Parent B had another child support case involving one child aged under 13.
- Multi-case allowance: both calculators calculated the same allowance of $4,599.
- Care input: care was entered as 6 nights out of 14.
- Reason for care change: using 6 nights out of 14 removed the care-entry issue from the earlier tests.
A multi-case allowance is an income adjustment. Once calculated, it reduces the relevant parent’s income before the normal child support formula is applied.
Only AusChildSupport and ChildSupportCalculator.au provided a way to handle a situation where a parent has multiple cases.
| Calculator | Multi-case allowance | Result | Test outcome |
|---|---|---|---|
| AusChildSupport | $4,599 | $5,660.51 per year | Calculated the allowance correctly, but the final result appears to reflect an internal formula-application error. |
| ChildSupportCalculator.au | $4,599 | $5,830 per year | Used a separate income adjustment calculator, then applied the adjusted income to the normal calculator. |
Both calculators calculated the same multi-case allowance of $4,599. The difference in the final result therefore did not come from the allowance calculation.
The care input was also controlled by using 6 nights out of 14 in both calculators. That removed the care-percentage issue from the earlier tests.
ChildSupportCalculator.au produced $5,830 per year after the adjusted income figure was entered into its normal calculator. The adjustment was visible, and the calculator had already matched the benchmark results in the earlier tests.
AusChildSupport produced $5,660.51 per year. It provided the smoother experience because the multi-case details were entered directly and the adjustment was handled behind the scenes. However, with the same allowance and the same care input, the lower final result points to an error in the calculator’s internal application of the child support formula after the allowance was calculated.
Speed and Ease of Use
The calculators differed in speed and workflow because they did not attempt the same functions. Some tools were fast because they asked for fewer details. Others were slower because they allowed more family circumstances to be entered. A more cumbersome process was not necessarily worse if the extra inputs enabled more cases to be handled.
| Calculator | Speed | Ease of use |
|---|---|---|
| Services Australia | Slowest. | Required names, dates of birth, and several responses about possible case complications. Going back to change inputs was awkward, and the calculator could time out and force a restart. |
| Unified Lawyers | Quick. | Simple to complete, but changes required pressing a submit button. Repeated testing was somewhat clunky compared with calculators that updated instantly. |
| Child Support Australia | Almost instant. | Easy to use for standard scenarios. No submit button was required after changing the main inputs. Relevant dependent child estimates required following instructions below the calculator. |
| Custody X Change | Almost instant. | Fast interface, but low usefulness because child ages could not be entered. Missing basic age inputs meant the outputs could never be trusted. |
| AusChildSupport | Slow. | More seamless for relevant dependent children and multi-case inputs, but the step-wise process was slow. Each child had to be added manually, with several options to consider before reaching the result. |
| ChildSupportCalculator.au | Almost instant. | Easy to use for standard scenarios. No submit button was required after changing the main inputs. Relevant dependent children and multi-case allowances were handled through separate adjustment calculators. |
Services Australia remained the official benchmark, but it was the least convenient tool for quick testing. Child Support Australia and ChildSupportCalculator.au were the fastest accurate calculators. AusChildSupport offered the most seamless entry for complex family details, but the slower step-wise workflow and hidden adjustments reduced confidence in the results.
Overall Calculator Assessments
Services Australia
The Services Australia estimator was used as the benchmark because it is the official calculator. It reproduced the standard formula result and the relevant dependent child result, but does not produce multi-case estimates. It was also the slowest and least convenient tool for scenario testing. The interface is old, and changing a scenario often requires going back through earlier screens. The calculator can also time out and return an error, forcing the user to start again. Users need to plan any test scenarios in advance rather than make quick adjustments on the fly.
Unified Lawyers
The Unified Lawyers calculator was quick to use, but it is a basic calculator despite its polished appearance. It could not reproduce the standard scenario exactly because care had to be entered as 6 nights out of 14 rather than as the rounded care percentage used in the official formula. For many ordinary cases, simple nights-per-fortnight input will be good enough. However, it limits precision when a scenario depends on the exact care percentage. It did not provide an option for adding a relevant dependent child or handling a multi-case allowance.
Child Support Australia
The Child Support Australia calculator is accurate and fast. It matched the Services Australia result in the standard formula test and matched the relevant dependent child result within $1 after following its written instructions. The calculator returns results almost instantly, with no submit button required after changing the main inputs. Its design appears to trade some built-in functionality for speed and ease of use. Relevant dependent children are handled through instructions below the calculator rather than a dedicated input field, and no built-in method was provided for the multi-case scenario tested. For standard estimates, it performed very well. For more complex cases, users may need to do an adjustment separately before using the calculator.
Custody X Change
The Custody X Change calculator was fast and easy to use, but the result was wholly unreliable. Child ages could not be specified, even though the Australian formula uses different cost values for children aged under 13 and children aged 13 to 17. Age is not an optional detail. It is a core formula input. No option was found for adding a relevant dependent child or handling a multi-case allowance. Because mandatory inputs were missing, the calculator could not reproduce Australian formula results in the tested scenarios and should not be used.
AusChildSupport
AusChildSupport provided the smoothest step-wise experience for more complex family circumstances. It allowed relevant dependent children and multi-case details to be entered directly, making it one of only two calculators tested that tackled the multi-case scenario. However, it produced higher results in the first two tests because care had to be entered as whole nights per fortnight. In the multi-case test, it calculated the same multi-case allowance as ChildSupportCalculator.au but produced a different final result, suggesting a problem with how the hidden adjustment was integrated into the formula.
ChildSupportCalculator.au
ChildSupportCalculator.au was the best calculator tested. It matched the Services Australia result in the standard formula test and matched the relevant dependent child result within $1 after using its income adjustment calculator. It was also one of only two calculators that handled the multi-case scenario. The calculator was fast, accurate, and capable across all three tests. Its main limitation was that dependent child and multi-case adjustments required separate calculators rather than built-in fields.