Child Support Calculator NZ 2025/26
Calculate NZ child support using the IRD formula. Both parents' incomes assessed. See how shared care nights affect your payment.
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How to Use This Calculator
Tab "Formula Assessment"
Enter both parents' annual incomes, the number of children (and how many are aged 13 or over), and the nights per year the children spend with the paying parent. The calculator applies the IRD formula to show your estimated annual child support, monthly payment, and per-child breakdown. You can also enter any other dependent children the paying parent supports, which reduces their assessable income.
Tab "Shared Care Impact"
Enter both parents' incomes and the number of children. The calculator shows how the child support obligation changes across five care scenarios — from no care to near-equal care (48%). Use this tab to understand the financial impact of different care arrangements before you negotiate.
Tab "Voluntary Agreement"
Enter the agreed amount and select the payment frequency. The calculator converts it to an annual equivalent and checks whether it meets the minimum threshold for IRD registration (~$910/year). A voluntary agreement must be registered with IRD to be legally enforceable.
The Formula
Assessable income = Gross annual income − Living allowance ($21,528 for 2025/26)
Step 2 — Adjust paying parent for other dependants:
Each other dependent child reduces the paying parent's assessable income
Step 3 — Child expenditure amount:
1 child = 18% of combined assessable income
2 children = 24% of combined assessable income
3+ children = 27% of combined assessable income
Children aged 13+ attract a 1.36× age loading
Step 4 — Each parent's share:
Paying parent's share = paying parent assessable income ÷ combined assessable income
Paying parent's liability = child expenditure amount × paying parent's share
Step 5 — Care cost offset:
0–27% nights: no offset
28–34% nights: partial offset (25%)
35–47% nights: shared care offset (50%)
48–52% nights: substantially equal care — near nil
53%+ nights: paying parent has majority care
Step 6 — Minimum assessment:
Minimum = $910 per year (if paying parent has assessable income)
Care percentage:
Care % = nights with paying parent ÷ 365 × 100
All figures from Inland Revenue (IRD) for the 2025/26 tax year. Child support is governed by the Child Support Act 1991 (NZ).
Example
One child, no shared care — paying parent earns $70,000
Paying parent earns $70,000. Receiving parent earns $35,000. One child under 13. No shared care (0 nights).
If this parent increases shared care to 35% (128 nights per year), the care cost offset reduces their annual payment by roughly 40–50%, saving thousands per year.
NZ Child Support — Key Facts 2025/26
| Item | Detail |
|---|---|
| Administered by | Inland Revenue (IRD) — not the Family Court |
| Governing law | Child Support Act 1991 |
| Living allowance 2025/26 | ~$21,528 per year |
| Minimum annual payment | ~$910 |
| Income percentages | 1 child: 18% / 2 children: 24% / 3+: 27% |
| Age loading (13+) | 1.36× expenditure for older children |
| Shared care threshold | 35%+ nights = care cost offset applies |
| Equal care threshold | 48–52% nights = substantially equal care |
| Voluntary agreements | Must be registered with IRD to be enforceable |
| Payment method | IRD collects and pays — direct payment possible by agreement |
| Review/variation | Annual review of paying parent's income; variation applications available |
| Formula reform | Current formula in place since 2015 |
How Shared Care Changes Everything
The biggest variable in NZ child support is the number of nights the children spend with the paying parent. The system recognises that when a parent provides hands-on care, they are directly spending on the child — so their formula liability is reduced.
The 35% threshold is the key milestone. Once the paying parent has the children for 128 or more nights per year (about 2–3 nights per week on average), a care cost offset applies that substantially reduces the payment. Many parents find it worthwhile to negotiate an arrangement that crosses this threshold.
At 48–52% care (near-equal time), the formula result approaches nil, reflecting the reality that both parents are already bearing roughly equal costs directly.
Care percentages are calculated over a full year (365 nights), so irregular arrangements — such as longer holidays with one parent — all count. Keep records of actual nights for any IRD review.
Both Incomes Matter
Unlike some overseas systems, the NZ formula assesses both parents' incomes. A receiving parent who earns a high income will see a lower child support assessment than one who earns nothing, all else being equal. This reflects IRD's view that both parents share financial responsibility for the child's upbringing proportional to their means.
IRD uses the most recent tax return income for each parent. If income has changed significantly — such as after a job loss, promotion, or return to work — either parent can apply for an administrative review or a departure from the formula.
Self-employed parents, those with rental income, or those receiving distributions from a family trust may have their income assessed differently by IRD, as the formula income may be adjusted to reflect true economic income.
Voluntary Agreements vs Formula
Parents who can agree on an amount have the option to register a voluntary agreement with IRD instead of using the formula assessment. The key advantages of a voluntary agreement:
- Can be higher or lower than the formula amount (subject to the minimum)
- Avoids IRD involvement in setting the amount
- More flexible — can include non-cash contributions or specific arrangements
- Once registered, IRD can collect and enforce it like any formula assessment
The minimum threshold for IRD to register an agreement is approximately $910 per year. Agreements below this amount are not registerable. Unregistered private arrangements have no IRD enforcement support.
Both parents can also apply to the Family Court for a departure order if the formula produces an unjust result in their circumstances — for example, in cases of very high income, significant assets, or unusual child-related costs.