12 Countries, One Engine: PayrollEx Expands to Australia

Beyond Europe and North America

Until now, PayrollEx covered eleven countries: nine in Europe (DE, AT, CH, BE, NL, LU, FR, ES, PT), the United Kingdom, and the United States. All of them share a common thread — they are the jurisdictions that global employers operating from a European or North American base encounter most frequently.

Australia changes the geographic scope. It is the first Asia-Pacific country on the platform, and it validates a claim the architecture has always made but never had to prove at this distance: that a regulation built for German Lohnsteuer and Spanish IRPF can handle the Australian Tax Office’s coefficient-based PAYG system without any engine modification.

The engine didn’t change. The API didn’t change. The test infrastructure didn’t change. What changed is the regulation package that sits on top.

What AU.Payroll Covers

The Australian regulation (AU.Payroll) covers the core statutory requirements for Australian payroll processing:

This is not a simplified model. The PAYG calculation uses the ATO’s published coefficient method — the same algorithm that every compliant payroll system in Australia must implement. The STP PayEvent generates the XML structure that a Digital Service Provider submits to the ATO.

The Coefficient Method: A Different Tax Model

Australian income tax withholding works differently from every European country on the platform. Where Germany uses a full algorithmic PAP (Programmablaufplan), the UK uses cumulative PAYE with tax codes, and Spain applies progressive IRPF brackets, Australia uses a coefficient-based approach.

The ATO publishes two coefficients per income bracket — a (factor) and b (offset) — for each tax scale. The weekly withholding formula is:

weekly_withholding = (earnings × a) − b

This is fundamentally different from progressive bracket systems where each income slice is taxed at a different marginal rate. The coefficient method pre-computes the effective tax for each bracket, making the per-payrun calculation simpler but requiring the regulation to carry a larger lookup table (six scales, each with multiple brackets and two coefficients per bracket).

For PayrollEx, this meant implementing a PaygAlgorithm that loads the correct scale based on the employee’s tax treatment, looks up the matching bracket, applies the coefficient formula, and scales between weekly and monthly amounts. The algorithm is extracted as a standalone calculator class that can be unit-tested independently of the payroll engine.

Superannuation: Employer-Only Social Security

Australia has no employee-side social security contributions in the European sense. There is no equivalent of German KV/PV/RV/AV, Dutch ZVW/WW, or Spanish Seguridad Social employee shares. Instead, Australia has the Superannuation Guarantee — a mandatory employer contribution to the employee’s retirement fund.

This creates an interesting asymmetry in the consolidation interface:

WT 7015 is legitimately zero for Australia. This is not a gap — it reflects the statutory reality. The consolidation interface handles it correctly because it normalizes meaning, not field presence. When a DACH+AU consolidated report shows employee social security, Australia contributes zero, and that is the correct answer.

The SGC rate for FY 2025–26 is 12% of Ordinary Time Earnings (OTE), capped at a maximum contribution base per quarter. Salary sacrifice amounts flow into a separate employer super contribution — they do not reduce the SGC base. These interactions are covered by dedicated integration tests.

STP Phase 2: Electronic Filing, Australian Style

Every country has its own electronic filing requirements. Germany has LStAnmeldung and BeitragsNachweis. France has DSN. The UK has RTI. Spain has Sistema RED. Australia has Single Touch Payroll.

STP Phase 2 requires employers to report payroll data to the ATO after each pay event — not monthly, not quarterly, but per payrun. The PayEvent XML (PAYEVNT.0004 2020) includes:

• Payer record: ABN, Withholding Payer Number, organisation name, W1 (gross payments), W2 (PAYG withheld)
• Employee records: TFN, name, date of birth, employment dates, tax treatment code
• Income streams: YTD gross, YTD tax withheld, income stream type, tax treatment
• Super entitlements: YTD superannuation guarantee, YTD OTE

The report aggregates year-to-date figures from 1 July (the Australian financial year start) through the current period. It follows the same XmlWriter pattern used for the German LStAnmeldung — the report script generates XML content, which is extracted via an XSL template and output as a structured file.

The PayEvent report generates the data XML. Signing, authentication, and transmission to the ATO are handled by the employer’s registered Digital Service Provider — that integration is outside the regulation scope.

Eight States, Eight Tax Rates

State payroll tax in Australia is an employer tax on total wages, with each state and territory setting its own rate and threshold. This is structurally similar to the US state income tax problem, but simpler: payroll tax is employer-only and threshold-based rather than progressive.

The regulation resolves the applicable state from the employee’s work location. When an employee relocates mid-month (tested in WT-TC6700-AU-Intramonth-Relocation), the engine’s time-splitting handles the state transition automatically — each sub-period uses the correct state’s rate and threshold.

36 Integration Tests

The AU regulation ships with 36 integration tests — full payrun executions against a live backend, not unit tests. They cover the same categories as every other country regulation:

Every test includes a README with the step-by-step arithmetic derivation — the test is the calculation record. This is the same test-driven compliance approach used across all twelve countries.

The boundary tests are worth highlighting: prorata tests cover an employee starting on the last day of the month (1/31 of salary) and exiting on the first day (1/31 of salary). These are the edge cases that break payroll systems that use approximate day-counting.

Five Reports

The regulation includes five reports — four PDF reports and one XML report:

Consolidation: Australia in the Matrix

With Australia, the consolidation interface now spans twelve countries and four currencies (EUR, CHF, GBP, USD, AUD). The same WT 7000–7030 contract that works for DACH and Benelux works for Australia — because the contract normalizes statutory meaning, not field names.

Adding Australia required zero changes to the consolidation layer. The country regulation defines its own WT 7000–7030 mappings (e.g., WT 7005 = PAYG + MLS + SFSS + WHM tax), tags them with the Consolidation cluster, and the existing consolidation reports pick them up automatically.

This is the architectural test that matters: can a new country join the cross-country reporting matrix without modifying any existing code? With twelve countries, the answer is proven.

What’s Next

Australia is the first step into Asia-Pacific. The architecture supports any country where payroll can be expressed as cases, wage types, collectors, and lookups — which is every country.

The current twelve countries cover the core jurisdictions for global employers operating from Europe, North America, and now Oceania. The consolidation matrix grows with each country, and the per-country test suite ensures that every regulation ships with proof.

See the Australia coverage in the coverage matrix, or compare all twelve countries side by side.