In 2020, the Department of Education issued a final Rule pursuant to notice-and-comment rulemaking which created the most far-reaching regulation on sexual harassment in educational institutions under Title IX to date. This Rule significantly limited the availability of administrative remedies for those experiencing sexual harassment in their educational institutions. While much has been said regarding the propriety of the substantive policy decisions advanced by the Department’s regulation, relatively little attention has been paid to the cost-benefit analysis (CBA) employed in the Rule. The Rule’s CBA found that the regulations would result in a net cost of tens of millions of dollars. In justifying their commitment to these cost-unjustified regulations, the Department relied only on a few non-quantified benefits. To make matters worse, the Department also disclaimed any responsibility to consider whether the Rule’s deregulatory policies would leave sexual harassment under-deterred. The 2020 Rule was arbitrary and capricious by reason of its faulty CBA. The Department’s failure to consider the costs associated with the Rule’s under-deterrent effects was an abrogation of their obligation to uphold Title IX’s preventative purpose.