The Internal Revenue Service in the US defines the tax gap as the ‘difference between the amount of tax that taxpayers should pay and the amount that is paid voluntarily and on time’. HM Revenue and Customs in the UK use ‘the difference between tax collected and the tax that should be collected … if all individuals and companies complied with both the letter of the law and HMRC’s interpretation of the intention of Parliament in setting law’. The tax gap is used as a measure of non-compliance with tax law. See also tax avoidance; tax evasion.