The cornerstone of every arbitral award is the quantum of damages awarded. Yet, the principal must be brought forward in time, and that procedure involves the application of interest. International treaties, Bilateral investment treaties (‘BITs’) and national legislations all have their views on interest. However, determining the exact rate of interest often comes down to a case-by-case basis, where both quantum experts and lawyers have their say. A multitude of different approaches have been deployed in international arbitration. These include recourse to borrowing rates, or theories like the ‘coerced loan’ or the ‘alternative investment’. This article overviews the main approaches regarding the rate of pre-award interest and questions their suitability. A potential portfolio approach and other alternatives are assessed in case of the alternative investment theory, to balance the deficiency of the risk-free rate. The article also discusses the future of Interbank rates, after the London Inter-Bank Offered Rate (‘LIBOR’) cessation.