The aim of the article is to present the current state of efforts to reform financial market indexes, with a particular reference to how the proposed changes would affect the money market. Financial market indexes must be reformed under a Regulation of the European Parliament “on indices used as benchmarks in financial instruments.” The article verifies the thesis about the existence of a conversion path for indexes that would not threaten the stability of the market and ensure legal continuity. In order to verify the thesis, the author studies documents published by regulators and benchmark administrators in order to present the debate on possible opportunities and threats to the financial market resulting from specific solutions proposed by various stakeholders. The methodology applied in the article includes economic and legal research for the assessment of proposals regarding the liquidity and stability of the financial market. The author highlights the possible consequences of benchmark transformation on the reliability of financial indicators applied to the valuation of loans and derivatives. The conclusions of the analysis cover two basic aspects. First, an optimal definition of the index and the related methodology is proposed. Second, the author identifies a conversion path that minimizes the risk of destabilizing the financial market. The index is optimally defined as based on actual transactions. In the absence of a sufficiently liquid underlying market, the definition requires the transaction base to be broadened. In the case of money market indexes, non-bank deposits need to be taken into account. The new index definition will lead to changes in the level and variance of the benchmark, which may threaten the stability of contracts concluded on the financial market. It is therefore necessary to ensure the parallel publication of indexes according to both the old and new methodology.