Methodology · AU-PAY-011
PAYG Withholding Calculator
Calculate PAYG withholding per pay from the official ATO statement-of-formulas coefficients, including the study-loan component, never annual tax divided by periods.
Engines and formulas
- E03 · PAYG withholding engine
The ATO statement-of-formulas method: y = a·x − b on weekly-equivalent earnings with schedule rounding, plus the Schedule 8 study-loan component. Never annual tax divided by pay periods (§13.16).
Registered formulas: F-PAYG-001 schedule formulas
Rule packs
Statutory values come only from versioned, hash-verified rule packs citing official sources. Current status of the packs this calculator can use:
- au-income-tax-2024-25active · v0.1.0
- au-income-tax-2025-26active · v0.1.0
- au-income-tax-2026-27active · v0.1.0
- au-medicare-2024-25active · v0.1.0
- au-medicare-2025-26active · v0.1.0
- au-medicare-2026-27active · v0.1.0
- au-stsl-2024-25active · v0.1.0
- au-stsl-2025-26active · v0.1.0
- au-stsl-2026-27active · v0.1.0
- au-super-guarantee-2024-25active · v0.1.0
- au-super-guarantee-2025-26active · v0.1.0
- au-super-guarantee-2026-27active · v0.1.0
- au-payg-withholding-2026-27active · v0.1.0
Verification
Engines carry boundary tests at every bracket edge, property-based tests, reconciliation invariants and, where official worked examples exist, tests that reproduce them exactly. The full source register is on the sources page.