This study investigates the financial flexibility and adjustment speed of listed firms’ capital structures in Nigeria to determine whether firms proactively adjust toward the target capital structure or if market imperfections limit their adjustment. An ex post facto design was used, with secondary firm-level data of listed firms in the Nigerian Exchange Group sourced from the Trading-View database being assembled into a panel of 684 firm-year observations (2006-2024). The debt-to-assets ratio was used to measure leverage, in addition to the debt-to-equity ratio, long-term debt-to-assets ratio, and long-term debt-to-equity ratio. Explanatory variables were leverage, profit margin, firm size, growth, asset turnover, and free cash flow per share. Fixed-effects regression with heteroscedasticity-robust standard errors was preceded by descriptive statistics, correlation analysis, and the Hausman test. Lagged leverage was positive and statistically significant, indicating that leverage was not immediately adjusted to the target level but approached it gradually over time at an estimated adjustment rate of 30.03%. Profitability and FCF per share were negatively related to leverage and positively related to firm size. The findings indicate that internal cash-flow flexibility continues to be a key determinant in the leverage management of Nigerian listed firms, which is a general statement of the capital-structure adjustment theory and frontier-market finance.