Child Support Calculator
Estimate NZ child support liability using the IRD 8-step formula. Factors in living allowance, dependent children, and share of care.
About this calculator
This calculator implements IRD child support 8-step formula from Inland Revenue (IRD). Last consulted 18 May 2026. Verify the figures yourself by following the link.
NZ Child Support formula parameters
FY 2026-27 IRD formula- •Living allowance (single): $30,557
- •Dependent child allowance: Cost-of-children % of income after living allowance
- •Cost of 1 child %: 17%
- •Cost of 2 children %: 24%
- •Cost of 3+ children %: 27%
- •Shared care threshold: 28% of nights (103+/yr)
- •Minimum annual liability: $1,211
Source: IRD — Child Support
Disclaimer
This calculator provides estimates for general information purposes only. Results should not be relied upon as professional financial, tax, or legal advice. Tax rates and thresholds are based on publicly available IRD data and may change. Always consult a qualified tax agent or financial adviser for advice specific to your circumstances.
How NZ Child Support is calculated (IRD 8-step)
ATI − living allowance × cost-of-children % × share-of-care reduction = liability.
- 1
Adjusted taxable income (ATI)
ATI = taxable_income + add-backs (rental losses, fringe benefits)
Uses prior tax year by default.
- 2
Living allowance
Living_allow = $30,557 single + ($10,500 if living with a new partner)
Indexed annually. A dependent child allowance is deducted separately (next step).
- 3
Child support income
CS_income = max(0, ATI − living_allow − dep_child_allow)
Dependent child allowance = cost-of-children % × (ATI − living allowance), for your other dependent children. If negative, only the minimum applies.
- 4
Cost of children %
Cost_% = 17% (1 child) / 24% (2) / 27% (3+)
Of CS_income.
- 5
Share of care reduction
Care_pct = nights ÷ 365 × 100 — recognised only at 28%+ of nights (103+/yr)
Below 28% (under 103 nights): no reduction. 28–34% = 24%, then increases with nights.
- 6
Final liability
Annual = max($1,211 minimum, base × (1 − care_reduction))
Minimum $1,211/yr (2026).
Worked example
Inputs: ATI $80k, single, 2 dep children, 1 CS child, 50 care nights
Result: Living allowance $30,557. Dependent-child allowance 24% × ($80k − $30,557) = $11,866. CS income $37,577. Base $37,577 × 17% = $6,388. Care 14% → no reduction. Annual ≈ $6,388.
Frequently Asked Questions
How is NZ child support calculated?
Can parents agree on a different amount?
The NZ child support calculator estimates your annual and monthly liability under Inland Revenue's formula assessment for 2026. It applies your adjusted taxable income, the $30,557 living allowance, the dependent-child allowance, cost-of-children percentages, and the shared-care reduction.
How this calculator works
IRD's formula starts with your adjusted taxable income (ATI) — normally last year's taxable income plus add-backs such as rental losses. From this it deducts a living allowance of $30,557 for a single parent, plus $10,500 if you live with a new partner, and a dependent-child allowance for other children in your care, calculated as the cost-of-children percentage of your income after the living allowance. What remains is your child support income. The cost-of-children percentage — 17% for one child, 24% for two, 27% for three or more — is applied to produce the base liability. If you care for the children at least 28% of nights (103 or more per year), a care-cost reduction applies, starting at 24% and rising with your share of care. The result can never fall below the statutory minimum of $1,211 per year.
IRD formula parameters 2026
| Living allowance (single parent) | $30,557 |
| Extra if living with a new partner | +$10,500 |
| Cost of children — 1 child | 17% of child support income |
| Cost of children — 2 children | 24% |
| Cost of children — 3+ children | 27% |
| Shared-care threshold | 28% of nights (103+/yr) |
| Care reduction at 28-34% of nights | 24% |
| Minimum annual liability | $1,211 |
Figures are indexed annually by IRD; this is the simplified formula — the full assessment may include other income types.
Worked Examples
ATI $80,000, single, 2 dependent children at home, 1 child on child support, 50 care nights
Annual liability ≈ $6,388 (about $532/month).
- Living allowance: $30,557
- Dependent-child allowance: 24% × ($80,000 − $30,557) = $11,866
- Child support income: $80,000 − $30,557 − $11,866 = $37,577
- Base liability (1 child): $37,577 × 17% = $6,388
- Care: 50 ÷ 365 = 14% of nights — below 28%, no reduction
- Annual ≈ $6,388, monthly ≈ $532
ATI $60,000, living with a new partner, no other dependents, 2 children on child support, 130 care nights
Annual liability ≈ $3,380 (about $282/month) after a 25.6% shared-care reduction.
- Allowances: $30,557 + $10,500 = $41,057
- Child support income: $60,000 − $41,057 = $18,943
- Base liability (2 children): $18,943 × 24% = $4,546
- Care: 130 ÷ 365 = 35.6% of nights → reduction ≈ 25.6%
- Liability: $4,546 × (1 − 0.256) ≈ $3,380 — above the $1,211 minimum
Built and maintained by Konstantin Iakovlev. Data sourced from the IRD and official New Zealand government sources.
Last reviewed: