Methodology
New Zealand GST Registration Decision Tool methodology
Educational only: Business decision support, not accounting, tax or legal advice.
Privacy: Calculations run locally; Margin101 does not receive your commercial inputs.
Update policy: Reviewed when formulas or official dependencies change.
Scope: New Zealand small-business planning using your own assumptions.
1. Formulas and units
Pᵢ = Pₑ × (1 + tₒ) when registered and tax-inclusive; otherwise Pᵢ = PₑWhere
- tₒ
- Selected source-versioned output GST rate (decimal rate)Source: Reviewed official rule · New Zealand GST standard rate
- Pₑ
- Required price excluding GST (NZD per unit)Source: Calculated output
- Pᵢ
- Required displayed price (NZD per unit)Source: Calculated output
Pₑ = Cₑ ÷ (1 − m)Where
- Cₑ
- Effective cost after recoverability treatment (NZD per unit)Source: Calculated output
- m
- Target retained margin (decimal rate)Source: User decision
- Pₑ
- Required price excluding GST (NZD per unit)Source: Calculated output
T = Pᵢ − PₑWhere
- Pₑ
- Required price excluding GST (NZD per unit)Source: Calculated output
- Pᵢ
- Required displayed price (NZD per unit)Source: Calculated output
- T
- GST component (NZD per unit)Source: Calculated output
Recoverable input tax: Cₑ = C ÷ (1 + tᵢ) when C is tax-inclusive, otherwise Cₑ = C. Non-recoverable input tax: Cₑ = C when C is tax-inclusive, otherwise Cₑ = C × (1 + tᵢ)Where
- C
- Entered cost on the confirmed GST basis (NZD per unit)Source: Business record
- Cₑ
- Effective cost after recoverability treatment (NZD per unit)Source: Calculated output
- tᵢ
- Confirmed input GST rate on the entered cost (decimal rate)Source: Business record
G = Pₑ − CₑWhere
- Cₑ
- Effective cost after recoverability treatment (NZD per unit)Source: Calculated output
- Pₑ
- Required price excluding GST (NZD per unit)Source: Calculated output
M = G ÷ PₑWhere
- Pₑ
- Required price excluding GST (NZD per unit)Source: Calculated output
ΔP = Pᵢ − P₀Where
- Pᵢ
- Required displayed price (NZD per unit)Source: Calculated output
tₒ = tⱼWhere
- tₒ
- Selected source-versioned output GST rate (decimal rate)Source: Reviewed official rule · New Zealand GST standard rate
R = 2 when a reviewed trigger applies; R = 1 at an equality boundary; otherwise R = 0Where
- R
- Authority-review signal (boolean status)Source: Calculated output
L = LᵣWhere
- L
- Reviewed official threshold (NZD)Source: Reviewed official rule · New Zealand GST registration threshold tests
T₁ = ΣT₁ᵢWhere
- T₁
- Taxable-activity turnover in the last 12 months (NZD)Source: Business record
T₂ = ΣT₂ᵢWhere
- T₂
- Expected taxable-activity turnover in the next 12 months (NZD)Source: User assumption
Tₕ = max(T₁, T₂)Where
- T₁
- Taxable-activity turnover in the last 12 months (NZD)Source: Business record
- T₂
- Expected taxable-activity turnover in the next 12 months (NZD)Source: User assumption
- Tₕ
- Highest entered turnover (NZD)Source: Calculated output
H = max(0, L − Tₕ)Where
- L
- Reviewed official threshold (NZD)Source: Reviewed official rule · New Zealand GST registration threshold tests
- Tₕ
- Highest entered turnover (NZD)Source: Calculated output
- H
- Remaining amount to threshold (NZD)Source: Calculated output
Money inputs and outputs use NZD. Rates, margins, utilisation and buffers are entered as percentages and converted to decimal values for calculation.
2. Worked example
Input assumptions
The default fixture sets a $60 cost, 40.0% target retained margin and a confirmed market policy branch. The price engine returns $115 displayed price and $40 gross profit per unit.
Calculation and outputs
Example
The default fixture sets a $60 cost, 40.0% target retained margin and a confirmed market policy branch. The price engine returns $115 displayed price and $40 gross profit per unit.
- Required displayed price
- $115
- Required price excluding GST
- $100
- GST component
- $15
- Effective cost
- $60
- Gross profit per unit
- $40
- Retained gross margin
- 40.0%
- Change from current displayed price
- $15
- Selected GST rate
- 15.0%
- Review status
- Below threshold
- Selected registration threshold
- $60,000
- Taxable-activity turnover in the last 12 months
- $0
- Expected taxable-activity turnover in the next 12 months
- $0
- Highest entered turnover
- $0
- Remaining to threshold
- $60,000
The registration engine separately compares $0 for taxable-activity turnover in the last 12 months with $0 for expected taxable-activity turnover in the next 12 months.
Interpretation
Use the New Zealand GST result as a bounded planning review, not a registration or tax determination.
3. Validation and boundary checks
- Turnover values must be finite, non-negative and use the official turnover scope.
- Cost, target margin, registration, jurisdiction/place-of-supply, supply/customer class and effective-date inputs must remain inside the supported source-versioned policy branch.
- Tax-inclusive and tax-exclusive price identities reconcile through the selected official rate; retained margin is measured on revenue excluding tax.
- Each supported period is compared independently; the engine never adds unlike periods together.
- Equality does trigger the selected rule, matching the reviewed authority wording.
- Unsupported business classes and unconfirmed turnover scope fail closed.
- The dependency version is returned by the policy contract and acknowledged in canonical tool history.
4. Assumptions and source classification
- The selected class is inside the bounded scope described by ird-gst-registration-threshold-nz.
- The user has excluded amounts that the authority excludes from the relevant turnover definition.
- The prospective value is a user-owned scenario, not a Margin101 forecast.
- The customer/transaction, jurisdiction and effective-date confirmations are user-owned classifications and are not inferred from names, addresses or dates.
- No below-threshold result overrides another statutory trigger or special rule.
Official dependencies used by this decision tool are captured in the Margin101 evidence register and version-acknowledged in this page history. User-entered commercial assumptions remain separate from those official inputs.
5. Limitations
- The tool does not decide registration, effective dates, deregistration, voluntary registration, taxability, exemptions, groups, cross-border treatment, place of supply or filing.
- The price result does not replace an invoice, accounting or tax-system calculation and supports only the displayed rate, supply, customer and jurisdiction branches.
- Only the displayed business classes and turnover tests are supported.
- The tool does not replace the authority guidance or professional advice.
This is educational decision support, not tax, accounting, legal or financial advice. Check the treatment of your actual transactions under the rules that apply in New Zealand and seek qualified advice where appropriate.
6. Update and evidence policy
Registered family-level suites test formula invariants and example reconciliation; the release ledger records that coverage without claiming a separate oracle for every line of public copy. Registered official sources block dependent public workflows when their evidence or version acknowledgement is unavailable or invalid. Commercial inputs remain user-supplied because they vary by business and contract.
Change history
- : Initial public release of the planner and methodology after pre-launch calculation, content, source and interaction review.
Related reading
Guides to interpret the decision and its assumptions.
- New Zealand GST Pricing: Final Price and Revenue
Separate retained revenue from New Zealand GST after registration and supply treatment have been independently confirmed.
Read guide