Child Support Calculator
A formula assessment is how Inland Revenue works out child support when the parents do not agree an amount. Enter each parent's income, the nights the child lives with one parent, and the ages of the children. The estimate uses the rates for 1 April 2026 to 31 March 2027.
The Formula Assessment
A formula assessment is Inland Revenue's calculation of who pays child support, and how much, under the Child Support Act 1991. It uses the child's age, both parents' incomes, the time the child lives with each parent, and the cost of raising a child. A qualifying child is a child that child support is paid or received for. A dependent child is a parent's own child who lives with them and is not in a child support assessment. A non parent carer's income is not part of the formula.
Inland Revenue takes allowances off each parent's income, adds what is left, and works out each parent's share of that combined child support income. It then turns nights of care into a care cost percentage. Income share minus care cost percentage is the child support percentage. A positive percentage means that parent pays. A negative percentage means that parent receives. The annual amount is the positive percentage times the cost of the children. Payments are due to Inland Revenue by the 20th of the following month, and Inland Revenue pays the receiving carer by the 23rd of that month.
Living Allowance and Child Support Income
Child support income starts with the income Inland Revenue will use, then takes off a living allowance. For 1 April 2026 to 31 March 2027 the standard living allowance is $30,557. A parent who receives a supported living payment uses $34,252 instead. If the allowances are as large as the income, or larger, that parent's child support income is nil. The inflation factor for this child support year is 3.1%.
| Part of the formula | 1 April 2026 to 31 March 2027 |
|---|---|
| Living allowance | $30,557 |
| Living allowance on a supported living payment | $34,252 |
| Minimum child support for the year | $1,211 |
| Inflation factor | 3.1% |
If the only income is salary, wages, a benefit, or other income taxed at source, Inland Revenue starts with taxable income from the last calendar year. If the parent files an IR3, Inland Revenue starts with net income from two tax years ago and adjusts it for inflation. Enter the figure after that step. This estimate does not add 3.1% on top of a number you have already inflated. A new partner's income is not in the formula. Child support and spousal maintenance received are not counted in the income used for this assessment.
A dependent child allowance and a multi group allowance can come off child support income as well. The dependent child allowance uses the same expenditure table, on that parent's income after the living allowance, for children who live with them and are not in this assessment. A multi group allowance recognises children in another child support group, with a cap so the parent does not pay more than if all the children lived together. Neither allowance is in this estimate.
Care and Who Pays
Recognised care is usually the nights a child regularly lives with a parent, in a year of 365 nights. Inland Revenue counts care in the formula once it is at least 28% of the time, which it describes as about 2 nights a week, or 103 nights a year. Less than that is counted as 0% care. To receive child support, the child needs to live with that parent for at least 35% of the time, about 5 nights a fortnight, or 128 nights a year. The percentage is rounded to a whole number.
| Share of care | Care cost percentage |
|---|---|
| 0% to 27% | 0% |
| 28% to 34% | 24% |
| 35% to 47% | 25%, plus 2 points for each point over 35% |
| 48% to 52% | 50% |
| 53% to 65% | 51%, plus 2 points for each point over 53% |
| 66% to 72% | 76% |
| 73% to 100% | 100% |
Those bands are Schedule 2 of the Child Support Act 1991. Inland Revenue's formula notes match the bands: care around 30% has a care cost percentage of 24%, and care of 37% has a care cost percentage of 29%. Care of 35% has a care cost percentage of 25%, and care of 65% has a care cost percentage of 75%. Four nights a week is about 57% care and a care cost percentage of 59%. Five nights a week is about 71% care and a care cost percentage of 76%. People still say care counts only after 3 nights a week. Inland Revenue's line is 28% for recognised care, and 35% before a parent can be paid.
The parent with more care can still be the one who pays, if their income share is higher than their care cost percentage and the other parent has at least 35% care. A parenting order or agreement is what Inland Revenue uses, unless both parents agree it is not being followed, or one parent shows that it is not. Daytime care, such as a boarding school, can still count. Tell Inland Revenue if the ongoing arrangement changes. Within 28 days, the record updates from the date of the change. After 28 days, it updates from the date you tell them. Use myIR, phone, or a change of circumstances form, IR116. A recognised care questionnaire is IR120.
The Cost of the Child
The cost of the children comes from Inland Revenue's child expenditure table for 1 April 2026 to 31 March 2027. The table uses average weekly earnings of $1,652.72. Combined child support income is split into bands, with a cap once income is over two and a half times that yearly figure, which is $214,855 and over. Children aged 12 or under and children aged 13 or over are different columns. A child turning 13 is a reason for a new assessment.
One child aged 12 or under costs 17 cents in the dollar up to $42,971, then $7,305 plus 15 cents in the dollar over $42,972, and the cost stops rising at $26,212. One child aged 13 or over costs 23 cents in the dollar up to $42,971, then $9,883 plus 22 cents in the dollar over $42,972, and the cost stops rising at $32,657. Two children, and three or more children, have their own columns. If the children are in both age groups, Inland Revenue says to look up the table using the total number of children, divide by that number for each age table, then add the children in each age group. This estimate does that. It assumes every child in the assessment has the same nights.
If the formula amount is more than zero and less than the minimum, the estimate uses $1,211 for the year. That is the minimum rate of child support for this child support year. There is no separate cap when there is only one child support group. A formula assessment is redone for the year from 1 April to 31 March, and it can also change when income or care changes.
Formula, Private Agreement, or a Benefit
Inland Revenue uses the formula when the parents cannot agree an amount, or are not on good terms. A private or voluntary agreement can be easier to change as circumstances change. If a carer gets an unsupported child's benefit for that child, they must apply for a formula assessment, and they cannot cancel it or switch agreement type while the child still qualifies and lives with them. Everyone in the application needs an IRD number. Proof of parentage can be a full birth certificate, or a written acknowledgement. A Family Court paternity order can backdate child support to the application date if the court application and the order are each given to Inland Revenue within 60 days.
Working for Families uses different care rules from child support. Child support looks at nights. The Working for Families calculator is a separate estimate, and it does not work out this payment. A formula assessment can end when someone no longer qualifies, when the receiving carer cancels it, or when the parents register a voluntary agreement instead. Source: Inland Revenue how formula assessments work, child support rates, child expenditure tables, and sharing care.
How to Read the Result
The result stays blank until you enter at least one child, both incomes, and the nights with parent A. Placeholders are only a hint. Parent B is given the other nights in a 365 night year. The large figure is the annual amount, with the monthly amount beside it, because Inland Revenue collects and pays child support by the month. The rows show each parent's child support income, income percentage, care percentage, and care cost percentage, then the cost of the children from the expenditure table.
A supported living payment tick uses the $34,252 living allowance for that parent. If the parent who would receive has under 35% care, the estimate is zero and the note says no one pays. If the formula is under $1,211 and someone still pays, the estimate lifts to that minimum. Dependent children, a second child support group, daytime care that is not overnight, and a change part way through the year are not in the total. Inland Revenue's own calculator is the assessment. This page applies the published formula to the figures you type.