Currently in Saudi Arabia, fast-growing companies are increasingly requiring debt portfolios which enable them to finance their rapid expansion without causing growth to become a situation that makes it hard to refinance afterwards. This study looks at how companies can improve their debt capital structures by striking a balance between three conflicting aims: the cost of capital, liquidity resilience, and financial risk. It is based on evidence from peer-reviewed publications between 2020 and 2025, with a focus on Saudi Arabia, the Gulf Cooperation Council markets and similar emerging markets, and incorporates insights from trade-off theory, pecking order theory, agency theory, signaling theory and the theory of dynamic calibration. The evidence indicates that there is no one leverage ratio that is optimal in all circumstances. Sustainable debt capacity is affected by profitability, the visibility of cash flow, firm size, the tangibility of assets, the availability of growth opportunities, debt maturity, market access and governance quality. Moreover, evidence obtained from Saudi Arabia shows that both the maturity of debt and the size of the firm have an impact on the relationship between leverage and performance. Meanwhile, the expanding sukuk and bond market is offering new possibilities for increasing maturities and for diversifying the investor base. The review recommends a portfolio-based method of optimization according to which companies should first examine their debt capacity in the case of stressed cash flows and then choose the appropriate instruments and maturities on the basis of the lifetime of their assets, their liquidity needs, the flexibility of any covenants, and the expected conditions for refinancing. The key conclusion is that high-growth firms in Saudi Arabia should regard leverage as a dynamic range backed by liquidity buffers, maturity ladders, and governance mechanisms which are activated by certain events, rather than as a fixed target ratio.