Calculate.co.nz NZ Calculators

nz_secondary_tax_calculator

Find the right New Zealand secondary tax code and what it costs.

Use for: 'what tax code for my second job', 'is secondary tax a rip off',
'why am I taxed so much on my second job', 'what is SH SL', 'do I get that
money back', filling in an IR330.

CORRECT THE MISCONCEPTION. A secondary code is not a penalty. It
approximates the marginal rate the second income attracts on top of the
first, so roughly the right amount comes out through the year, and any
excess comes back in the year-end square-up. year_end_position says which
way it falls for this person, and a refund is common and normal.

The rates look brutal because they are not income tax rates: each carries
the 1.75% ACC earner levy, and the SL codes add 12% student loan on top. So
31.75% is 30 plus 1.75, not a 31.75% tax rate. The response breaks the rate
into its components; use them when explaining.

ALWAYS ask for the main job income. The code depends on the two incomes
combined, so an answer without it is a guess.

Args:
    main_income: Gross annual income from the main job.
    secondary_amount: The second income, in the frequency given.
    secondary_frequency: annual, monthly, fortnightly or weekly.
    has_student_loan: Changes the code to its SL variant.

Returns:
    The IR330 code, the flat rate broken into its parts, what is deducted
    and what is left, and the estimated year-end bill or refund from these
    two sources.

Input Schema

TableJSON Schema

Name	Required	Default
`main_income`	Yes
`has_student_loan`	No
`secondary_amount`	Yes
`secondary_frequency`	No	annual

Schema Changelog

Changes observed during successful MCP inspections.

First observedSep 1, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are present, so the description carries the full burden, and it compensates by correcting the misconception that secondary tax is a penalty and explaining that rates include ACC and student loan components. It also tells the agent how to interpret and explain the output, which is behavioral context beyond the schema.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is longer than average, but the extra length earns its place by addressing a widespread misconception and giving agent-facing explanation guidance. The structure is clear: use cases, conceptual correction, parameter list, and return summary.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no annotations and no output schema, the description covers the key invocation context: when to use, what to ask for, what each parameter means, and what the response contains. It is not exhaustive, such as lacking an explicit when-not-to-use, but it is sufficient for an agent to select and call the tool correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, but the Args section supplies meaningful descriptions for all four parameters, including the frequency options and student loan effect. It lacks input validations such as positivity or currency, but enough semantics are provided for correct invocation.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: finding the right New Zealand secondary tax code and what it costs. The 'Use for' examples with concrete user questions make the tool's scope unambiguous and distinguish it from generic tax calculators among siblings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides explicit trigger phrases for when to use it and instructs the agent to always ask for main job income, since the code depends on both incomes. It does not explicitly list exclusions or alternatives, but the use cases and prerequisites give clear directional guidance.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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