<p>In this study, biodiesel production was carried out using oils obtained from fish processing waste of <i>Sarda sarda</i> and <i>Scomber scombrus</i> species. To monitor the quality changes during the storage of the produced biodiesel at room temperature (22 ± 2&#xa0;°C) for 60&#xa0;days, the Dynamic Fuel Integrity Index (DFII) was defined as an index that allows monitoring quality changes during the storage process. The DFII was designed to reflect the total effect of oxidative degradation, changes in fatty acid structure, and compositional imbalances experienced by the biodiesel during storage. Three dynamic parameters derived from temporal changes in peroxide value, free fatty acid content, and PUFA/MUFA ratio were considered in the index calculation: change in oxidative load (Δ_ox), fatty acid shear score (Δ_xa), and compositional flux instability (Δ_flux). By combining these parameters, a single integrity value ranging from 0 to 100 was obtained, with DFII values ​​below 60 interpreted as a critical level of quality loss for biodiesel. DFII decreased from 100 to 43.17 (<i>Sarda sarda</i>) and to 46.34 (<i>Scomber scombrus</i>) over 60&#xa0;days, indicating earlier integrity loss for <i>Sarda sarda</i>.</p> Graphical Abstract <p></p>