# Fix an incorrect result [#fix-an-incorrect-result]

Use this guide when a TaxKit result appears to disagree with an official
source, a published example or a known scenario.

## Before you start [#before-you-start]

* Reproduce the calculation with the public SDK or HTTP API.
* Capture the input facts, calculator ID, jurisdiction, tax year and report.
* Find the owning package with
  [What are you changing?](/contributing/what-are-you-changing).

Do not patch an HTTP response or SDK helper to mask a tax result. Incorrect
tax behaviour belongs in the owning fact, rule, parameter, calculator or
catalogue boundary.

## Diagnosis [#diagnosis]

Work from evidence:

1. Compare the result with an official source or known scenario.
2. Inspect trace output and source references.
3. Identify the first incorrect fact, parameter, rule or ledger component.
4. Add a failing golden test or regression test before the fix.
5. Fix the owning package.
6. Re-run compatibility tests if public API or SDK output changes.

## Tests [#tests]

Your evidence should include:

* the failing scenario before the fix
* a golden test or regression test that would fail without the fix
* trace or ledger evidence when rule order or component values changed
* type tests when public input types changed
* API compatibility tests when HTTP output or errors changed
* SDK compatibility tests when SDK output or errors changed

## Pull request evidence [#pull-request-evidence]

Your PR must include source citations, the failing and passing test evidence,
compatibility notes and release-impact notes. Use
[PR evidence checklist](/contributing/pr-evidence-checklist).