Methodology · AU-PAY-011
How the PAYG Withholding Calculator works
This page documents how the PAYG Withholding Calculator produces its figures: the engines and formulas it runs, the rule packs it reads statutory values from, the official documents those packs cite, and how the engines are verified. Official sources were last retrieved on .
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
- Tax rates - Australian residentsAustralian Taxation Office · retrieved 2026-08-20
- Tax rates - foreign residentsAustralian Taxation Office · retrieved 2026-08-20
- Low income tax offsetAustralian Taxation Office · retrieved 2026-08-20
- Tax rates – working holiday maker (2024–25 table)Australian Taxation Office · retrieved 2026-08-21
- au-income-tax-2025-26active · v0.1.0
- Tax rates - Australian residentsAustralian Taxation Office · retrieved 2026-08-20
- Tax rates - foreign residentsAustralian Taxation Office · retrieved 2026-08-20
- Low income tax offsetAustralian Taxation Office · retrieved 2026-08-20
- Tax rates – working holiday maker (2025–26 table)Australian Taxation Office · retrieved 2026-08-21
- au-income-tax-2026-27active · v0.1.0
- Tax rates - Australian residentsAustralian Taxation Office · retrieved 2026-08-20
- Schedule 15 - Tax table for working holiday makersAustralian Taxation Office · retrieved 2026-08-20
- Low income tax offsetAustralian Taxation Office · retrieved 2026-08-20
- au-medicare-2024-25active · v0.1.0
- Medicare levy surcharge income, thresholds and ratesAustralian Taxation Office · retrieved 2026-08-20
- Medicare levy reduction for low income earnersAustralian Taxation Office · retrieved 2026-08-20
- Medicare levy reduction - family incomeAustralian Taxation Office · retrieved 2026-08-20
- Tax rates - Australian residentsAustralian Taxation Office · retrieved 2026-08-20
- myTax 2025 — Medicare levy reduction or exemption (2024-25 thresholds)Australian Taxation Office · retrieved 2026-08-21
- Medicare levy reduction — family income (2024-25)Australian Taxation Office (via web.archive.org capture 2025-09-19) · retrieved 2026-08-21
- au-medicare-2025-26active · v0.1.0
- Medicare levy surcharge income, thresholds and ratesAustralian Taxation Office · retrieved 2026-08-20
- Medicare levy reduction for low income earnersAustralian Taxation Office · retrieved 2026-08-20
- Medicare levy reduction - family incomeAustralian Taxation Office · retrieved 2026-08-20
- Tax rates - Australian residentsAustralian Taxation Office · retrieved 2026-08-20
- au-medicare-2026-27active · v0.1.0
- Medicare levy surcharge income, thresholds and ratesAustralian Taxation Office · retrieved 2026-08-20
- Medicare levy reduction for low income earnersAustralian Taxation Office · retrieved 2026-08-20
- Medicare levy reduction - family incomeAustralian Taxation Office · retrieved 2026-08-20
- Tax rates - Australian residentsAustralian Taxation Office · retrieved 2026-08-20
- au-stsl-2024-25active · v0.1.0
- Study and training support loans rates and repayment thresholdsAustralian Taxation Office · retrieved 2026-08-20
- au-stsl-2025-26active · v0.1.0
- Study and training support loans rates and repayment thresholdsAustralian Taxation Office · retrieved 2026-08-20
- au-stsl-2026-27active · v0.1.0
- Study and training support loans rates and repayment thresholdsAustralian Taxation Office · retrieved 2026-08-20
- au-super-guarantee-2024-25active · v0.1.0
- Super guarantee percentage and maximum contribution baseAustralian Taxation Office · retrieved 2026-08-20
- au-super-guarantee-2025-26active · v0.1.0
- Super guarantee percentage and maximum contribution baseAustralian Taxation Office · retrieved 2026-08-20
- au-super-guarantee-2026-27active · v0.1.0
- Super guarantee percentage and maximum contribution baseAustralian Taxation Office · retrieved 2026-08-20
- au-payg-withholding-2026-27active · v0.1.0
- Schedule 1 - Coefficients for withholding from weekly payments (from 1 July 2026)Australian Taxation Office · retrieved 2026-08-20
- Schedule 8 - Statement of formulas for calculating STSL componentsAustralian Taxation Office · retrieved 2026-08-20
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.