Corporate Accounting and Financial Management · Cost of Capital

Marginal Cost of Capital: Meaning and Calculation

Updated 11 October 2026 · Fact-checked

Marginal cost of capital (MCC) is the weighted average cost of the next rupee of new capital a company raises. You find it by using current costs of each source and the target capital structure weights. Break points show where MCC rises because a cheaper source runs out.

Understand Marginal Cost of Capital

A company does not raise all its money at one cost. The first lot of cheap funds, such as retained earnings, gets used up. After that, it must raise costlier funds, such as new equity shares with flotation costs, or debt at a higher interest rate.

Marginal cost of capital (MCC) is the cost of raising one more rupee of new capital. It is a weighted average, but it uses the cost of the new funds and the target proportions in which you will raise them. It looks forward, not at what the company raised in the past.

It differs from WACC as usually calculated. WACC often uses the existing book or market weights and the historic cost of funds already in the capital structure. MCC uses the cost of new funds at the margin. If costs stay constant, the two can be the same. In practice, MCC usually rises as more capital is raised.

MCC rises in steps. Each source has a limit up to which it is available at a given cost. The total new capital at which a source's cheap limit ends is the break point. After the break point, the weight-adjusted cost goes up.

The MCC schedule is used in capital budgeting. You compare it with the IRR of projects, ranked from the highest return downward. You accept projects as long as the IRR is above the MCC. The point where the two cross gives the optimal capital budget.

Key rules to remember

Marginal cost of capital: MCC = Σ (Wᵢ × Kᵢ); Wᵢ is the target weight of each source in the new capital. Kᵢ is the cost of that source for the new funds.
Break point: Break point = Amount of cheaper source available ÷ Weight of that source in the capital structure; It is the total new capital that can be raised before that source's cost increases. For example, retained earnings of ₹30,00,000 at a weight of 60% give a break point of ₹50,00,000.
Cost of debt (after tax): Kd = I × (1 − t) ÷ NP, or Kd = r × (1 − t) for debt issued at par with no costs; Use the after-tax cost because interest is tax-deductible. t is the tax rate.
Cost of equity (dividend growth): Ke = D₁ ÷ P₀ + g, or D₁ ÷ NP + g for new shares after flotation cost; D₁ is next year's expected dividend. For new equity, use net proceeds in place of the market price.
Cost of retained earnings: Kr = D₁ ÷ P₀ + g; Use the market price with no flotation cost, unless the question says to adjust for personal tax or brokerage.
Investment decision rule: Accept a project if IRR > MCC; The optimal capital budget is the amount of projects that clear this test.

How to solve Marginal Cost of Capital questions

Use this method for any question that asks for marginal cost of capital, break points or the optimal budget.

1Write down the target capital structure weights for debt, preference and equity. These are the weights for new capital.
2List each source with the amount available at each cost level. Note when the cost changes, for example after retained earnings are exhausted or debt exceeds a limit.
3Calculate the cost of each source at each level. Take debt after tax, and use net proceeds for new issues.
4Compute break points for every source whose cost changes: amount available at the lower cost ÷ weight.
5Arrange the break points in ascending order. This gives the ranges of total new capital, for example ₹0 to ₹50 lakh, then ₹50 lakh to ₹80 lakh, and so on.
6For each range, calculate the weighted cost using Σ (W × K) with the cost of each source applicable in that range. This is the MCC for that range.
7If the question gives projects, rank them by IRR, compare each with the MCC for its range, and accept those whose IRR is above the MCC. The cumulative investment gives the optimal capital budget.
8State the conclusion clearly in one line, with the range and the rate.

Quickest way: Break point table method

When to use it: Use this when the question gives limits on cheap funds and asks for MCC at different amounts of new capital.

Compute the break points first, before any weighted cost. Write them as a column.
Create one row per range between break points.
In each row, change only the source whose cheap limit has ended. Keep the other costs as they were.
Compute Σ (W × K) for each row and write the MCC beside it.
Match projects against these rows and stop at the last project whose IRR is above the MCC.

Common mistakes in Marginal Cost of Capital

Using book value or existing weights instead of target weights
Students carry over the WACC habit of using the balance sheet.
Fix: For MCC, always use the target or proposed proportions of the new capital. Read the question for the word target, proposed or optimum.
Forgetting to use the after-tax cost of debt
The pre-tax interest rate is given prominently and looks like the cost.
Fix: Multiply by (1 − tax rate) every time unless the question says the company pays no tax.
Dividing the available amount by the cost instead of the weight when finding break points
Students mix up the two percentages in the table.
Fix: Break point = available amount of the source ÷ its weight in the capital structure. Cost is never used here.
Missing a break point after the first one
Students stop once they see one jump in cost and ignore other sources whose cost also changes.
Fix: Check every source for a limit. Compute all break points and sort them before building the ranges.
Using the same cost of equity for retained earnings and new shares
Both use the dividend growth formula, so students skip the flotation cost.
Fix: Retained earnings have no flotation cost. New equity shares use net proceeds, so their cost is higher.
Comparing project IRR with the overall WACC instead of the MCC for the relevant range
Students stop after the first rate they calculate.
Fix: Compare each project with the MCC at the cumulative investment level. The MCC can be higher for later projects.

Worked examples

Example 1

A company wants to keep a capital structure of 40% debt and 60% equity. It expects to have retained earnings of ₹30,00,000 available this year. The cost of retained earnings is 15% and the cost of new equity shares is 18%. The after-tax cost of debt is 6% for all amounts. Find the break point and the marginal cost of capital before and after it.

Show the solution

Break point = Retained earnings ÷ Equity weight = ₹30,00,000 ÷ 0.60 = ₹50,00,000.
Range 1: total new capital up to ₹50,00,000. Equity comes from retained earnings at 15%.
MCC in range 1 = (0.40 × 6%) + (0.60 × 15%) = 2.4% + 9.0% = 11.4%.
Range 2: total new capital above ₹50,00,000. Equity comes from new shares at 18%.
MCC in range 2 = (0.40 × 6%) + (0.60 × 18%) = 2.4% + 10.8% = 13.2%.

Answer: The break point is ₹50,00,000. MCC is 11.4% up to ₹50,00,000 and 13.2% above it.

Example 2

A company has the target structure of 50% debt and 50% equity. Retained earnings available are ₹20,00,000 at a cost of 14%. New equity costs 16%. Debt costs 5% after tax up to ₹30,00,000 and 7% after tax above that. The company has these projects: A needs ₹30,00,000 with IRR 15%; B needs ₹30,00,000 with IRR 12%; C needs ₹20,00,000 with IRR 9%. Decide which projects to accept.

Show the solution

Break point for retained earnings = ₹20,00,000 ÷ 0.50 = ₹40,00,000.
Break point for cheap debt = ₹30,00,000 ÷ 0.50 = ₹60,00,000.
Range 1: up to ₹40,00,000. MCC = (0.50 × 5%) + (0.50 × 14%) = 2.5% + 7.0% = 9.5%.
Range 2: ₹40,00,000 to ₹60,00,000. MCC = (0.50 × 5%) + (0.50 × 16%) = 2.5% + 8.0% = 10.5%.
Range 3: above ₹60,00,000. MCC = (0.50 × 7%) + (0.50 × 16%) = 3.5% + 8.0% = 11.5%.
Rank projects by IRR: A (15%), B (12%), C (9%).
Project A uses the first ₹30,00,000, which is in range 1 where MCC is 9.5%. IRR 15% is above 9.5%, so accept.
Project B takes cumulative investment from ₹30,00,000 to ₹60,00,000, which falls in ranges 1 and 2 with MCC of 9.5% and 10.5%. IRR 12% is above both, so accept.
Project C takes cumulative investment from ₹60,00,000 to ₹80,00,000, which falls in range 3 with MCC of 11.5%. IRR 9% is below 11.5%, so reject.

Answer: Accept projects A and B and reject C. The optimal capital budget is ₹60,00,000.

Exam tips

Show the break point calculation as a separate line. Examiners give marks for the method even if a later figure is wrong.
Present the MCC in a small schedule with range, source costs, weights and MCC. It is clear and easy to check.
Write one line on the difference from WACC, because theory questions often ask it: MCC uses the cost of new funds at target weights, while WACC often uses existing capital.
End project questions with a clear decision statement and the optimal capital budget in rupees.
Check the question for words that change costs, such as flotation cost, tax rate and limits on debt.

Practice questions from Cost of Capital

Marginal Cost of Capital in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Marginal Cost of Capital: frequently asked questions

What is the difference between WACC and marginal cost of capital?

WACC is the average cost of the funds a company already uses, often weighted by book or market value. MCC is the weighted cost of the next rupee of new capital, using current costs and target weights. MCC usually rises as the company raises more funds.

What is a break point in marginal cost of capital?

A break point is the total amount of new capital at which a cheaper source of funds runs out and its cost rises. You find it by dividing the amount available from that source by its weight in the capital structure. At each break point, the MCC steps up.

Why does marginal cost of capital increase?

Cheap sources have limits. Retained earnings are limited by profit, and lenders ask for higher rates on larger loans. Once these are used up, the company must raise costlier funds, such as new equity with flotation cost.

How is marginal cost of capital used in capital budgeting?

You rank projects by IRR and compare each with the MCC at that level of total investment. You accept a project while its IRR is higher than the MCC. The total of accepted projects is the optimal capital budget.