From the Executive Summary and Introduction: "President Biden recently proposed the American Families Plan, advancing comprehensive and necessary investments in American children and families. To help support this important agenda and increase fairness in the tax system, the President also proposed a set of tax compliance measures to foster a tax system where Americans pay the taxes they owe. This report describes the President's tax compliance initiatives that seek to close the 'tax gap'--the difference between taxes owed to the government and actually paid. According to Treasury analysis, the tax gap totaled nearly $600 billion in 2019 and will rise to about $7 trillion over the course of the next decade if left unaddressed--roughly equal to 15% of taxes owed. These unpaid taxes come at a cost to American households and compliant taxpayers as policymakers choose rising deficits, lower spending on necessary priorities, or further tax increases to compensate for the lost revenue."
U.S. Department of the Treasury: https://home.treasury.gov/