This study examines the influence of mental accounting, financial attitudes, financial knowledge, and financial self-efficacy on the financial behavior of diligent students in using fintech. This study differs from previous research because it uses a sample of students who already have a business and often use fintech. Data collection was carried out through the distribution of questionnaires to respondents. This study found that financial attitudes and self-efficacy had a significant effect on financial behavior, while financial knowledge had no significant effect on financial self-efficacy and mental accounting. Mental accounting significantly affects financial attitudes, financial behavior, and financial self-efficacy. These findings prove the importance of mental accounting in increasing the confidence and effectiveness of students who often use fintech and have a business in making financial decisions. This research contributes to developing the theory of planned behavior in the context of financial behavior. It reveals that financial literacy does not necessarily increase financial self-efficacy and mental accounting, especially among students who often use fintech and are just starting a business.