Guaranteed interest is crucial in financial systems, boosting depositor confidence and impacting bank risk. The discussion about guaranteed interest has been thorough, focusing on the reassurance it provides to depositors and the risks it brings. Although it prevents bank running, it can also make depositors too relaxed, potentially causing future crises. Previous research has focused on established guaranteed interest schemes, but there is still a gap in understanding the impact of introducing guaranteed interest during a crisis. This paper explores the relationship between guaranteed interest and managerial behavior, customers, and performance of conventional and Islamic banking. The research design uses existing statistics, with data obtained from the publications of the Financial Services Authority and Bank Indonesia. The analysis uses VAR/VECM models, with results showing that the movement of guaranteed interest rates (both rupiah and foreign currency) has a dominant impact on conventional banking compared to Islamic banking, both on bank managerial behavior, customer behavior, and the performance of the bank itself. Specifically, the movement of the guaranteed interest will trigger the management of conventional banks to increase loan interest, while from the customer side they will ask for a higher yield (interest) on third part funds (TPF). As a result, these two things will lead to a negative outcome on the performance of the bank itself, especially on Net Interest Margin (NIM), Return on Assets (ROA), Operational Expenditure to Operational Income (BOPO), and Loan to Deposit Ratio (LDR). In Islamic banks, the movement of the guaranteed interest also has an impact on the managerial behavior of the bank, customer behavior, and the performance of the bank itself, but the effect of the movement of the guaranteed interest is only small. Most of the growth in credit and deposits, fluctuations in financing margins and returns on deposits and dominant Islamic Financial Performance for Banking indicators are explained by factors other than movements in guaranteed interest rates.