4. United Kingdom — PAYE, National Insurance and HMRC Certificates

The United Kingdom engine previews PAYE and National Insurance Contributions through the uk_calc.go calculator. Notably, this calculator ships with unit tests, reflecting the care taken over the tax and NIC arithmetic that determines each employee's deductions.

The engine produces the standard set of United Kingdom payroll documents:

  • P60 — the end-of-year certificate summarising an employee's pay and deductions for the tax year.
  • P45 — the leaver certificate issued when an employee leaves employment.
  • P11D — the return of benefits in kind.
  • EPS — the Employer Payment Summary.

These outputs map to the real rhythm of United Kingdom payroll administration. The P60 closes out the tax year for continuing employees, while the P45 handles departures — making it the counterpart of the lifecycle resignation and termination actions in the HR module. The P11D captures taxable benefits that sit outside ordinary salary, and the Employer Payment Summary reports employer-level figures to the tax authority.

As with the other jurisdictions, the United Kingdom engine reads from the same payroll runs produced by the core engine, so PAYE and NIC previews and the end-of-year and leaver certificates are all derived from the organisation's actual pay data rather than being maintained separately.