One of the most significant international taxation trends has been the rise of thin capitalization rules. However, these rules are one of many legislative approaches to restricting interest deductibility, and since 2015, a new trend has emerged. Increasingly, jurisdictions across Europe and Asia are replacing their thin capitalization rules with fixed-ratio rules in accordance with the OECD BEPS Action 4 recommendation for a net interest-to-EBITDA ratio. Yet, governments are not always able to observe how multinational enterprises structure their internal affairs in response to regulatory changes. Therefore, this article presents a case study of the United Kingdom’s corporate interest deductibility rules over the past 3 decades and analyses these reforms by simulating the behavioural responses of a tax-minimizing multinational enterprise. This review and analysis both facilitate a comparison of the effectiveness of these rules in the UK context, which can inform the framing and evaluation of such regimes in other jurisdictions.