Research and analysis

Tax complexity project

These documents set out conclusions from OTS research into ways to measure complexity in the tax system.

This was published under the 2010 to 2015 Conservative and Liberal Democrat coalition government



We’ve been thinking about ways to measure complexity in the tax system. These documents set out our conclusions.

Developing a tax complexity index in the UK

This paper was presented at the International Tax Analysis Conference and sets out the methodology for the OTS tax complexity index.


On 4 December 2012 we published a paper setting out the methodology for the complexity ‘index’. The methodology has been developed to show which parts of tax legislation are particularly complex.

Tax thresholds

On 18 December 2012 we published a paper on the numerical tax thresholds in UK tax legislation. The paper looks at the number, value and age profile of the 639 thresholds. A significant proportion of the thresholds are penalties. The value of thresholds ranges from thousandths of a penny to £20 billion.

Length of tax legislation

On 16 April 2012 we published a short paper on the length of tax legislation. The paper concludes that length of legislation is a factor that contributes to complexity, but the issue is more complex than a simple page count. Although there are 17,795 pages in the Tolley’s Yellow and Orange books for 2011/12, we found that on closer analysis there are only 6,102 pages of substantive direct and indirect tax legislation.

Responses to tax complexity index methodology

Following the publication of the tax complexity index methodology, we received several thoughtful responses. Professor David Ulph of St. Andrews University has written a paper on tax complexity in which he discusses what complexity is and critiques our measure. Richard Baron of the Institute of Directors has also written a critique of the methodology, and David Pett of Pett, Franklin and Co. (also a member of our Employee share schemes review Consultative Committee) has suggested a tweak to the index weighting.

Published 8 February 2013
Last updated 28 February 2014 + show all updates
  1. Developing a tax complexity index for the UK paper added
  2. Tax complexity index methodology paper – second version published
  3. First published.