<p>Children should only be claimed on a single tax return, but some are claimed on two returns, or double-claimed. While many countries use child registries to prevent double-claiming, the United States tax authority does not. As a result, in 2001 the U.S. had over one million double-claimed dependents. Despite increasing child tax benefit values, the number of double-claimed dependents in the U.S. decreased by 80% over the last two decades. </p><p>This paper documents this decrease and suggests it partly resulted from an increase in electronically filed returns, as double-claiming causes automatic e-file rejections. The decrease in double-claimed dependents avoids over 50,000 annual audits and reduces annual tax credit payments by about $3&#xa0;billion. Our findings suggest e-filing may have helped lower tax noncompliance more broadly over this period, as the IRS also rejects e-filed returns for many other reasons. Additionally, double-claiming illustrates a consequence of tax complexity, as dependent-claiming rules are often not straightforward. This analysis is also timely. There have been two recent proposals for U.S. child registries, and the IRS just reversed its longstanding policy to now allow e-filed double-claiming.</p>