Tax gap methodology

In Australian tax gaps 2015–16, we published our latest tax gap estimates for goods and services tax (GST), wine equalisation tax (WET), luxury car tax (LCT), petrol and diesel excise and duty, pay as you go (PAYG) withholding, and fuel tax credits (FTC).

This document provides further information about the methodologies we use, including:

  • key gap concepts and ideas
  • how we calculate the voluntary compliance ratio
  • the broad approaches we use to estimate each gap
  • the limitations of our approaches.

For each gap, we provide our methodology, data sources and key assumptions. The limitations specific to each gap and the reliability of the estimate are also provided.

The process of gap estimation is a technically complex task that, in essence, is the measurement of the unmeasurable. Our scope, methods, data and estimates will continue to evolve, and revisions and restatements to the estimates are likely to occur in future releases.

We are committed to publishing a comprehensive suite of gap measures covering the taxes and programs we administer. We will continue to add to our suite of gap estimates over time.

If you require further detail or wish to provide feedback, contact us at

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    Last modified: 27 Oct 2016QC 50394