Buy Now, Pay Later (BNPL) has emerged as a rapidly growing form of installment-based digital credit in the United States, often marketed as a flexible and inclusive alternative to traditional borrowing. This dissertation examines how BNPL functions within the financial lives of consumers facing structural financial constraints, with particular attention to perceived financial well-being and financial capability. Using a mixed-methods design, the study integrates a quantitative analysis of U.S. adults with a qualitative focus-group study of financially constrained young adults. The findings show that the relationship between BNPL use and perceived financial well-being varies meaningfully by income: frequent use is associated with lower perceived financial well-being among low- and middle-income consumers, while no significant association is observed among higher-income users. Qualitative findings further reveal that BNPL is understood and navigated primarily through experiential learning, belief-based financial knowledge, and social context, enabling short-term financial flexibility and, in some contexts, generating longer-term strain. Together, the studies show that BNPL operates as a context-dependent financial tool whose implications depend on income, financial buffers, and the alignment between access to credit and consumers' ability to manage repayment obligations. The dissertation offers contributions to research and theory by reframing BNPL as a context-dependent financial tool, and to practice by highlighting how product design and access structures shape consumers' ability to manage repayment obligations over time.