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Xearno Tools

UK High Income Child Benefit Charge (HICBC) Optimizer

uk_child_benefit_charge
Read-only

How much of your child benefit the £60k–£80k charge claws back — and the exact pension contribution that makes it disappear. Computes the High Income Child Benefit Charge on the higher earner’s adjusted net income (ANI): 1% of the household’s child benefit per £200 of ANI above £60,000, reaching 100% at £80,000. Then it computes the lever most people miss — relief-at-source pension contributions are grossed up ×1.25 before they reduce ANI, so a precise net contribution can zero the charge while collecting higher-rate relief on top. General AI still quotes the old £50,000 threshold, cites the household-income reform that was announced and then dropped, and tells you Self Assessment is required when PAYE collection has been live since September 2025.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
giftAidNoGift Aid donations this year (net) (£) Charity donations under Gift Aid (what you actually gave). Like pensions, they are grossed up ×1.25 and reduce adjusted net income.
childrenNoChildren you claim child benefit for Eldest child £27.05/week, each additional child £17.90/week (2026-27).
higherIncomeNoHigher earner’s taxable income (£) The HIGHER earner’s adjusted-net-income components before this tool’s deductions: salary + bonus + benefits in kind (company car, medical) + rental and investment income. The charge always tests the higher partner individually — never the household total.
pensionContributionsNoPension contributions this year (relief at source, net) (£) What you actually paid into a personal/workplace relief-at-source pension (the net amount). The provider adds 25% basic-rate relief, and the GROSSED-UP figure (×1.25) reduces your adjusted net income — this is the lever that shrinks or zeroes the charge. Salary-sacrifice and net-pay contributions are already out of your taxable income, so leave those out.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A4.6/5.0
Behavior5/5

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

Discloses key behaviors beyond readOnlyHint: formula details, gross-up factor, individual earner focus, and exclusions (salary-sacrifice). Adds significant context beyond annotations.

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?

Front-loaded with key results, then provides background and warnings. Slightly verbose but each sentence adds value. Well-structured.

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

Completeness5/5

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

No output schema, but description explains both outputs (charge amount and optimal pension contribution) and the underlying formula. Covers important contextual warnings (outdated advice).

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?

Adds meaning beyond schema by explaining the 'lever most people miss' and clarifying which contributions count. Schema coverage is 100%, but description provides extra nuance.

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?

The description clearly states it computes the HICBC and the exact pension contribution to eliminate it. It distinguishes itself from sibling financial calculators by addressing a specific UK tax charge.

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 clear use case and warns about common misconceptions (old threshold, dropped reform, PAYE vs Self Assessment). Does not explicitly list when not to use, but context is strong.

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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