When a company raises its first ₹10 crore of capital, one cost applies. When it raises the next ₹10 crore, a different — usually higher — cost kicks in. That incremental cost is the Marginal Cost of Capital (MCC). Think of it like borrowing from a bank: your first loan is at 10%, but if you keep borrowing, the bank gets nervous and charges 12% on the next tranche. MCC captures exactly that shift.
In practice, MCC equals the Weighted Average Cost of Capital (WACC) calculated using the costs applicable to each new rupee raised — not the historical costs of capital already sitting on the balance sheet. The key trigger for MCC rising is the Break Point. A Break Point is the total new capital raised at which the cost of one or more components increases. The most common Break Point arises when retained earnings are exhausted: once a firm has used up all its internal accruals, it must issue new equity to maintain its target capital structure. New equity always costs more than retained earnings because of flotation costs (underwriting fees, issue expenses). The formula is straightforward — Break Point = Amount of funds available from a cheaper source ÷ Proportion of that source in the capital structure.
Beyond the Break Point, the WACC steps up to a new, higher level — this stepped-up WACC is the MCC for that range of financing. If you plot total new capital on the X-axis and WACC on the Y-axis, you get a staircase-shaped MCC Schedule — flat, then a step up, flat again, then another step. The firm should keep raising capital only as long as the return on new investment (the Marginal Return on Investment / IRR) exceeds the MCC. The optimal capital budget is where these two curves intersect. This intersection concept is asked frequently as a 5–8 mark question in Paper 6, especially in the context of combining capital budgeting with cost of capital.