2.4.9 Assessments when a parent has multiple child support cases (Formulas 3 & 4)
Context
Formula 3 is used to calculate the child support assessment when one or both parents have more than one child support case.
If somebody other than a parent is providing some care for a child and one or both parents have multiple child support cases then Formula 4 is used to calculate the assessment for that case.
Act references
CSA Act section 7B, section 36 to section 38, section 41, section 42, section 46 to section 48, section 55A to section 55E, section 55HA, section 156
On this page
Parents can have more than one child support case, that is, they can have children from different relationships in child support assessments with more than one other parent. To recognise a parent's responsibility to support their children in another child support case, one of the following mechanisms will be used to calculate child support assessments for parents with multiple child support cases:
 the multicase allowance, which is deducted from a parent's ATI to reach their child support income at step 1 of the basic formula (section 47), or
 the multicase cap, which is a separate calculation for the paying parent worked out at step 8 (section 55E).
For each child, a child support amount will be worked out using each of these 2 mechanisms, and the lesser of the 2 amounts will be the assessed rate of child support. Only one mechanism functions at a time  either the child support is worked out using the income after the deduction of the multicase allowance, or the child support is worked out according to the multicase cap on child support.
 Multicase child costs
 Multicase allowance
 Multicase cap
 Multicase allowance or multicase cap
 Formula 3  Parents in multiple child support cases
 Formula 4  Multiple child support cases with a nonparent carer
 When child support is payable by or to more than one person under Formula 4
Multicase child costs
Both the multicase cap and the multicase allowance are calculated using the multicase costs of the children.
The multicase costs of a child are what it would cost the parent to support the child if all of the parent's child support children lived with them fulltime, based on that parent's income.
When calculating the multicase costs, use the parent's ATI for the child support case, less the selfsupport amount and less the relevant dependent child amount (where appropriate).
The multicase cost of each child is calculated as if all the child support children were the same age as that child. To work out this cost:
 work out the total number of the parent's child support children
 look up the parent's (individual) income and the age of the child on the relevant Costs of the Children Table (2.4.2) to find what all the children would cost if they were all the same age
 divide this amount by the total number of the parent's child support children.
Note: 'The parent's child support children' are all of the children currently in the child support assessments of the parent for whom you are calculating the multicase costs.
The approach used to calculate the multicase costs of a child, although similar, differs from the multiple case method (2.4.6) of calculating the costs of a child. This is because the multicase costs recognise a parent's responsibility for all their children in all their child support cases, whereas the multiple case method calculates a parent's child support responsibility for the child or children in a case.
Example: Jonah has an initial child support income of $20,000 (the ATI less the selfsupport amount). Jonah and Sian have 2 children, Koby aged 14 and Ryan aged 10. Jonah has another child support case with Winfried for child Bran, aged 5. The multicase child costs for Koby and Ryan would be:
Costs of Koby (14 years old)
= $20,000 × $0.32 (3+ children aged 13+ years from the Costs of the Children Tables)
= $6,400 ÷ 3 (divide by number of all child support children)
= $2,133
Costs of Ryan (10 years old)
= $20,000 × $0.27 (3+ children aged 0 to 12 years from the Costs of the Children Tables)
= $5,400 ÷ 3 (divide by number of all child support children)
= $1,800
Multicase allowance
The multicase allowance is an allowance deducted from a parent's ATI to recognise a parent's responsibility for child support for their children in another child support case (section 47).
The multicase allowance is the sum of the multicase child costs, excluding the costs of the children of the case to which the assessment relates. That is, the parent has an amount deducted from their income to recognise the costs of supporting the children in their other case or cases. The amount deducted is the total of the multicase costs of those other children.
Example: Julie has children from 3 relationships. Julie and Charlton have 2 children, Jesse and Kevin. Julie and Josef have one child, Patricia. Josef also has an assessment with Hildegard for their children, Debi and Raul. Julie and Ruben have 2 children, Reginald and Jaron.
In calculating Julie's child support income for the assessment for Jesse and Kevin, the multicase allowance is the sum of the multicase costs of Patricia, Reginald and Jaron.
In calculating Julie's child support income for the assessment for Patricia, the multicase allowance is the sum of the multicase costs of Jesse, Kevin, Reginald and Jaron. Josef will also have a multicase allowance, being the multicase costs of Debi and Raul.
In calculating Julie's child support income for the assessment for Reginald and Jaron, the multicase allowance is the sum of the multicase costs of Jesse, Kevin and Patricia.
A parent can meet the costs of each child by paying child support, by directly caring for the child or by a combination of the 2. The multicase allowance recognises the costs of a child in another case, not the amount of child support payable.
The multicase allowance is rounded to the nearest dollar (section 156).
Example: Sam has an initial child support income of $20,000 (the ATI less the selfsupport amount). Sam has no relevant dependent children. Sam and Marisol have 2 children, Moses aged 14 and Adel aged 10. Sam has another child support case with Hiawatha for child Augustine, aged 5. In calculating the assessment for Augustine, the multicase allowance for Moses and Adel is the total of the multicase costs for Moses and Adel. The costs are as calculated in the example above.
Child support income for Sam
Multicase allowance = multicase costs of Moses + Adel
= $2,133 + $1,800
= $3,933
Initial child support income less the multicase allowance
= $20,000 − $3,933
= $16,067
Multicase cap
The multicase cap is used to ensure that the paying parent does not pay more child support for a child than they would if all the children lived in the same household. The cap recognises that the parent may be bearing some of the costs of a child directly through regular or shared care, and is adjusted accordingly. The cap is calculated on a per child basis.
The multicase cap for each child is the multicase child costs for the child, multiplied by the costs that the parent does not meet directly through care (100% less their cost percentage) (section 55E). That is:
(100% − cost percentage) × multicase child costs.
Example: If Edward has regular care of child Irene, and therefore a cost percentage of 24% for Irene, and Irene's multicase child cost is $1,800, then:
Multicase cap = (100% − 24%) × $1,800
= 76% × $1,800 = $1,368
Multicase allowance or multicase cap
The multicase allowance recognises a parent's responsibility to their other child support children by using an income shares approach. The multicase cap ensures a parent does not pay more for a child than they would if all children were living in the one household. Both the cap and the allowance are methods of recognising the parent's other obligations, so only one method is needed at any one time.
Only one method will be used to determine the child support amount payable for each child, i.e. either the child support amount is worked out using the income after the deduction of the multicase allowance, or the child support is worked out according to the multicase cap. For each child, the lesser of the 2 amounts calculated will be the assessed rate of child support.
Formula 3  Parents in multiple child support cases
This formula is used to work out the annual rate of child support payable for a child when one or both of the parents have at least one other case, and there is no nonparent carer (section 37).
Step 1: Work out each parent's child support income (2.4.7) (section 41), by using the following formula:
 parent's ATI in that child support case
 less the selfsupport amount
 less the parent's relevant dependent child amount (if applicable)
 less the parent's multicase allowance for the child.
Where a parent has more than one child support case, their child support income needs to be calculated separately for each case, as the parent's ATI and multicase allowance may differ across their child support cases.
First, take the parent's ATI applicable to that child support case and deduct the selfsupport amount.
Second, if applicable, work out a relevant dependent child (2.4.6) amount (section 46), and deduct the relevant dependent child amount from the amount above.
Third, if the parent has more than one child support case, work out the parent's multicase allowance (section 47) and deduct the multicase allowance from the amount above.
The final result is the parent's child support income for that case.
Step 2: Work out the parents' combined child support income (2.4.7) (section 42).
Step 3: Work out each parent's income percentage (2.4.7) (section 55B).
Step 4: Work out each parent's percentage of care (2.4.5) for the child (section 48).
Step 5: Work out each parent's cost percentage (2.4.5) for the child (section 55C).
Step 6: Work out each parent's child support percentage (2.4.5) for the child (section 55D).
Step 7: Work out the costs of the child (2.4.6) for the day under section 55HA, calculating the costs for older and younger children separately.
Step 8: If a parent has a positive child support percentage under step 6, the annual rate of child support payable by the parent for the child is worked out using the formula:
Child support percentage × costs of the child
The outcome of step 8 will be the child support payable if the parent assessed to pay child support does not have more than one child support case.
Step 9 (if applicable): If a parent has more than one child support case and a positive child support percentage under step 6, calculate the multicase cap for that parent (section 55E):
Multicase cap = (100% − Parent's cost percentage (2.4.5) for the particular child) × Multicase child costs for the particular child
The child support payable for the child is the lower of the annual rate calculated at step 8, or the multicase cap calculated at step 9.
Example: Formula 3 calculations
Vincent and Faith have 2 children, Geraldine aged 14 and Thomas aged 10. Vincent has another child support case with Sigrid for child Honoria, aged 5. Vincent has an ATI of $45,000 and Sigrid has an ATI of $40,000. Calculate the assessment for Honoria, who lives mostly with Sigrid, for a child support period commencing on 26 August 2008. Vincent has regular care of Honoria, providing care for 75 nights a year. Neither parent has any relevant dependent children.
Step 1: Work out each parent's child support income  Vincent  Sigrid  

Work out each parent's ATI for this case  $45,000  $40,000  
Deduct the selfsupport amount  −$18,252  −$18,252  
Deduct a relevant dependent child amount, if applicable  N/A  N/A  
Determine multicase child costs for each of the children in each parent's other child support cases:
Multicase cost of each child 
Costs of Geraldine (14 years old) $26,748 × $0.32 (fraction of MTAWE = 0.5, children aged 13+ years, 3+ children) ÷ 3 = $2,853 Costs of Thomas (10 years old) 
N/A  
Deduct a multicase allowance amount:

− ($2,853 + $2,407) = −$5,260 
N/A  
Each parent's child support income  = $45,000 − $18,252 − $0 − $5,260 = $21,488 
= $40,000 − $18,252 − $0 − $0 = $21,748 

Step 2: Work out the combined child support income  Vincent  Sigrid  
Each parent's child support income  $21,488  $21,748  
Combined child support income  = $21,488 + $21,748 = $43,236 

Step 3: Work out each parent's income percentage  Vincent  Sigrid  
Each parent's child support income Divide by the combined child support income Multiply the resulting amount by 100 Each parent's income percentage 
$21,488 ÷ $43,236 × 100 = 49.70% 
$21,748 ÷ $43,236 × 100 = 50.30% 

Step 4: Work out each parent's percentage of care  Vincent  Sigrid  
Each parent's care percentage To work this out, see 2.2.1. 
75 nights = 20.55% Rounded to = 20% 
290 nights = 79.45% Rounded to = 80% 

Step 5: Work out each parent's cost percentage  Vincent  Sigrid  
Each parent's cost percentage To work this out, see the Cost percentage table in 2.4.5. 
= 24%  = 76%  
Step 6: Work out each parent's child support percentage  Vincent  Sigrid  
Each parent's income percentage Deduct each parent's cost percentage Each parent's child support percentage 
49.70% − 24% = 25.70% 
50.30% − 76% = −25.70% 

A parent who has a positive child support percentage will need to pay child support. This means that Vincent is responsible for 49.70% of Honoria's costs because Vincent has 49.70% of the combined child support income. As Vincent meets only 24% of the costs through care, Vincent needs to transfer 25.70% of the costs to Sigrid through child support.  
Step 7: Work out the costs of each child  Honoria  
Combined child support income  $43,236  
Using the relevant Costs of the Children Table, calculate the total costs of the child (for Honoria: 2008, fraction of MTAWE = 1, children aged 0 to 12 years, one child) 
= $4,654 + ($0.15 for every $1 over $27,378) = $4,654 + (($43,236 − $27,378) × $0.15) = $4,654 + ($15,858 × $0.15) = $4,654 + $2,379 = $7,033 

Step 8: Work out the annual rate of child support payable by the parent with a positive child support percentage  Vincent  
Vincent's child support percentage Multiply by the total costs of the children Amount of child support for each child 
25.70% × $7,033 = $1,807 

If the parent has more than one child support case, follow the next step.  
Step 9 (if applicable): Work out the multicase cap  Vincent  
Work out the multicase child costs for the children in the child support case:
Multicase cost for Honoria 
Costs of Honoria (5 years old) $26,748 × $0.27 (fraction of MTAWE = 0.5, children aged 0 to 12 years, 3 children) ÷ 3 = $2,407 

Work out the multicase cap for Honoria: (100% − cost percentage) × multicase child costs for Honoria 
= (100% − 24%) × $2,407 = 76% × $2,407 = $1,829 

As the amount calculated at Step 8 ($1,807) is less than the multicase cap ($1,829) calculated at Step 9, the Step 8 amount is payable. Vincent is liable to pay Sigrid child support for Honoria of $1,807 (annual rate). 
Formula 4  Multiple child support cases with a nonparent carer
This formula is used to work out the annual rate of child support payable for a child when one or both of the parents have at least one other case, and one or more nonparent carers has at least 35% care of a child (section 38).
Step 1: Work out each parent's child support income (2.4.7) (section 41), by using the following formula:
 Parent's ATI in that child support case
 less the selfsupport amount
 less the parent's relevant dependent child amount (if applicable)
 less the parent's multicase allowance for the child.
Where a parent has more than one child support case, their child support income needs to be calculated separately for each case, as the parent's ATI and multicase allowance may differ across their child support cases.
First, take the parent's ATI applicable to that child support case and deduct the selfsupport amount.
Second, if applicable, work out a relevant dependent child (2.4.6) amount (section 46), and deduct the relevant dependent child amount from the amount above.
Third, if the parent has more than one child support case, work out the parent's multicase allowance (section 47) and deduct the multicase allowance from the amount above.
The final result is the parent's child support income for that case.
Step 2: Work out the parents' combined child support income (2.4.7) (section 42).
Step 3: Work out each parent's income percentage (2.4.7) (section 55B).
Step 4: Work out each parent's and nonparent carer's percentage of care (2.4.5) for the child (section 48).
Step 5: Work out each parent's and nonparent carer's cost percentage (2.4.5) for the child (section 55C).
Step 6: Work out each parent's child support percentage (2.4.5) for the child (section 55D).
Step 7: Work out the costs of the child (2.4.6) for the day under section 55HA, calculating the costs for older and younger children separately.
Step 8: If a parent has a positive child support percentage under step 6, the annual rate of child support payable by the parent for the child for the day is worked out using the formula:
Child support percentage × costs of the child
The outcome of step 8 will be the child support payable if the parent assessed to pay child support does not have more than one child support case.
Step 9 (if applicable): If a parent has more than one child support case and a positive child support percentage under step 6, calculate the multicase cap for that parent (section 55E):
Multicase cap = (100% − parent's cost percentage (2.4.5) for the particular child) × multicase child costs for the particular child
The child support payable is the lower of the annual rate calculated at step 8, or the multicase cap calculated at step 9.
Example: Formula 4 calculations
Aliya and Edmund have 2 children, Kristina aged 14 and Harriette aged 10. Aliya has another child support case with Marcus for child Claudia, aged 7. Aliya also has another child Louisa, aged 4, living with them. There is no assessment for Louisa. Aliya has an ATI of $45,000 and Edmund has an ATI of $70,000.
Calculate the assessment for Kristina and Harriette for a child support period commencing on 26 August 2008. Kristina lives full time with Edmund and Harriette lives full time with a grandparent Ali. Ali has made an application under section 25A for a child support assessment.
Step 1: Work out each parent's child support income  Aliya  Edmund  

Work out each parent's ATI for this case  $45,000  $70,000  
Deduct the selfsupport amount  −$18,252  −$18,252  
Deduct a relevant dependent child amount, if applicable. To work this out, see 2.4.4.20.  Costs of Louisa (4 years old) −($45,000 − $18,252) × $0.17) = −($26,748 × $0.17) (fraction of MTAWE = 0.5, children aged 0 to 12 years, one child) = −$4,547 
N/A  
Determine multicase child costs for each of the children in each parent's other child support cases:
Multicase cost of each child 
Costs of Claudia (7 years old
$22,201 × $0.27 (fraction of MTAWE = 0.5, children aged 0 to 12 years, 3+ children) ÷ 3 = $1,998 
N/A  
Deduct a multicase allowance amount: sum of the multicase child costs for the children of the other case/s 
−$1,998  N/A  
Each parent's child support income  = $45,000 − $18,252 − $4,547 − $1,998 = $20,203 
= $70,000 − $18,252 − $0 − $0 = $51,748 

Step 2: Work out the combined child support income  Aliya  Edmund  
Each parent's child support income  $20,203  $51,748  
Combined child support income  = $20,203 + $51,748 = $71,951 

Step 3: Work out each parent's income percentage  Aliya  Edmund  
Each parent's child support income Divide by the combined child support income Multiply the resulting amount by 100 Each parent's income percentage 
$20,203 ÷ $71,951 × 100 = 28.08% 
$51,748 ÷ $71,951 × 100 = 71.92% 

Step 4: Work out each parent's percentage of care for each child  Aliya  Edmund  
Each parent's care percentage To work this out, see 2.2.1. 
Aliya has 0% care of Kristina.  Aliya has 0% care of Harriette.  Edmund has 100% care of Kristina.  Edmund has 0% care of Harriette. 
Step 5: Work out each parent's cost percentage for each child  Aliya  Edmund  
Each parent's cost percentage To work this out, see the Cost percentage table in 2.4.5. 
Aliya has a cost percentage of 0% for Kristina.  Aliya has a cost percentage of 0% for Harriette.  Edmund has a cost percentage of 100% for Kristina.  Edmund has a cost percentage of 0% for Harriette. 
Step 6: Work out each parent's child support percentage for each child  Aliya  Edmund  
Each parent's income percentage  28.08%  71.92%  
Deduct each parent's cost percentage  − 0% for Kristina  − 0% for Harriette  − 100% for Kristina  − 0% for Harriette 
Each parent's child support percentage  = 28.08% for both Kristina and Harriette  = −28.08% for Kristina  = 71.92% for Harriette  
A parent who has a positive child support percentage will need to pay child support.
This means that Aliya is responsible for 28.08% of the costs of Kristina and Harriette, because Aliyah has 28.08% of the combined child support income. As Aliya does not meet any of the costs through care, they need to transfer 28.08% of the costs to the carers through child support. Edmund is entitled to receive child support from Aliya for Kristina and is required to pay child support for Harriette. 

Step 7: Work out the costs of each child  Kristina (14 years old)  Harriette (10 years old)  
Combined child support income of the parents  $71,951  $71,951  
Using the relevant Costs of the Children Table, calculate the total costs of the child  (for Kristina: 2008, fraction of MTAWE = 1.5, children aged 13+ years, 2 children) = ($15,606 + ($0.25 for every $1 over $54,756)) ÷ 2 = ($15,606 + (($71,951 − $54,756) × $0.25)) ÷ 2 = ($15,606 + ($17,195 × $0.25)) ÷ 2 = ($15,606 + $4,299) ÷ 2 = $19,905 ÷ 2 = $9,953 
(for Harriette: 2008, fraction of MTAWE = 1.5, children aged 0 to 12 years, 2 children) = ($12,868 + ($0.20 for every $1 over $54,756)) ÷ 2 = ($12,868 + (($71,951 − $54,756) × $0.20)) ÷ 2 = ($12,868 + ($17,195 × $0.20)) ÷ 2 = ($12,868 + $3,439) ÷ 2 = $16,307 ÷ 2 = $8,154 

Step 8: Work out the annual rate of child support payable by the parent with a positive child support percentage  Kristina (Aliya is liable to pay Edmund) 
Harriette (Both Aliya and Edmund are liable to pay Ali, as they both have positive child support percentages for Harriette) 

Aliya  Edmund  
Paying parent's child support percentage Multiply by the costs of the children Amount of child support for each child 
28.08% × $9,953 = $2,795 
28.08% × $8,154 = $2,290 
71.92% × $8,154 = $5,864 

If the parent has more than one child support case, follow the next step.  
Step 9 (if applicable): Work out the multicase cap  Kristina (This step is applicable only to Aliya) 
Harriette (This step is applicable only to Aliya) 

Work out the multicase child costs for the children in the child support case:
See instructions above in Step 1. 
Multicase costs of Kristina (14 years) = ($45,000 − $18,252 − $4,547) × $0.32 ÷ 3 
Multicase costs of Harriette (10 years) = ($45,000 − $18,252 − $4,547) × $0.27 ÷ 3 

Work out the multicase cap for each child:
(100% − cost percentage) x multicase child costs 
= (100% − 0%) × $2,368 = 100% × $2,368 = $2,368 As the amount calculated at step 8 ($2,795) is more than the multicase cap ($2,368) calculated at Step 9, the multicase cap is payable by Aliya. 
= (100% − 0%) × $1,998 = 100% × $1,998 = $1,998 As the amount calculated at step 8 ($2,290) is more than the multicase cap ($1,998) calculated at Step 9, the multicase cap is payable by Aliya. 

Child support payable  Aliya is liable to pay Edmund child support for Kristina of $2,368 (multicase cap).
Aliya is liable to pay Ali child support for Harriette of $1,998 (multicase cap). Edmund is to pay Ali child support for Harriette of $5,864 (annual rate). Ali is entitled to receive $1,998 + $5,864 = $7,862. 
When child support is payable by or to more than one person under Formula 4
If …  then … 
Example


both parents have a positive child support percentage at step 6 of the formula calculations  both parents pay child support to the nonparent carer/s (section 38(5)). 
The first parent, Ted, has a child support percentage of 83.47%. The second parent, Rita, has a child support percentage of 16.53%.
The costs of the child are $1,000. Both parents are required to pay child support to Valerie, who has fulltime care of the child. Ted will pay $1,000 × 83.47% = $835. Rita will pay $1,000 × 16.53% = $165. 
one parent has a positive child support percentage at step 6, and the other parent has:
a nil or negative child support percentage, and less than shared care 
only the first parent pays child support to the nonparent carer/s (section 38(5)). 
The first parent, Arnold, has a child support percentage of 83.47%. The second parent, Olivia, has regular care of the child and a child support percentage of −7.47% (16.53% − 24%).
The costs of the child are $1,000. Arnold is required to pay child support to Robert, who has primary care of the child. Arnold will pay $1,000 × 83.47% = $835. 
one parent has a positive child support percentage at step 6, and the other parent has:
a negative child support percentage, and at least shared care 
the first parent pays child support to the second parent and the nonparent carer (section 38(6)). The child support payable will be divided between the second parent and the nonparent carer by calculating their respective cost percentage as a proportion of their combined cost percentage. 
The first parent, Marcela, has a child support percentage of 83.47%. The second parent Frederique, has 37% care of the child (shared care) which is a cost percentage of 29% and a child support percentage of −12.47 (16.53% − 29%).
The nonparent carer, June, has 49% care of the child (shared care) which is a cost percentage of 50%. The costs of the child are $1,000. Marcela is liable to pay $1,000 × 83.47% = $835 in total. Marcela is required to pay child support to Frederique, using Frederique's cost percentage divided by the combined cost percentages of Frederique and June. Marcela will pay 835 × 29% ÷ (29% + 50%) = $307 to Frederique. Marcela is required to pay child support to June using June's cost percentage divided by the combined cost percentages of June and Frederique. Marcela will pay 835 × 50% ÷ (29% + 50%) = $528 to June. 
A nonparent carer is not entitled to be paid child support unless they have at least 35% care of the child (section 7B) and they have applied under section 25A (section 40B). If more than one nonparent carer is entitled to receive child support from a parent or both parents, then their share of the entitlement is determined in accordance with section 40A. See 2.4.8 for information about the calculations required when child support is payable to more than one person.
Different rules apply if the minimum annual rate of child support is payable to more than one person. See 2.4.12 for details of the rules that apply, which depend upon the level of care provided by the carer.