What Is WACC? Interview Answer for Investment Banking Recruits

WACC shows up the moment you say the word DCF. Interviewers ask what it is, how you build it, and what happens when it changes. Undergrads who memorized the formula without the intuition freeze on follow-ups. This is the deeper version that survives HireVue, first rounds, and a skeptical superday interviewer.

30-second answer

"WACC is the weighted average cost of capital. It is the blended return required by debt and equity holders, weighted by their proportions in the capital structure. In an unlevered DCF I discount free cash flow to firm at WACC to get enterprise value. Cost of equity usually comes from CAPM. Cost of debt is the after-tax yield on debt because interest is tax deductible."

The formula

WACC = (E / (D + E)) × Ke + (D / (D + E)) × Kd × (1 − t)

Where:

• E = market value of equity (not book)
• D = market value of debt when available (book often used as proxy in interviews)
• Ke = cost of equity
• Kd = pre-tax cost of debt
• t = tax rate

If preferred stock matters, add a preferred term with its own cost and weight. Most undergrad interviews stay with debt and equity.

Why market weights

Investors care about opportunity cost based on what capital is worth today, not what it was worth when booked years ago. Using book equity can understate equity weight for a profitable firm trading above book and distort WACC.

CAPM in one line

Ke = Rf + β × ERP

• Rf: long-term government yield (often cited as the 10-year; some use longer-duration matches)
• β: sensitivity to market returns; levered beta includes financial risk
• ERP: extra expected return for equities over the risk-free rate

Beta hygiene

• Levered beta reflects business risk + leverage
• Unlevered beta strips financial risk for peer comparison
• Relever beta at the target's target capital structure when building WACC from comps

Interview sentence: "I unlever peer betas to compare operating risk apples to apples, then relever at the target capital structure I am assuming in the DCF."

You do not need perfect mechanical recall of every unlever formula variant in HireVue. You do need the concept.

What WACC is conceptually

WACC is the discount rate for cash flows available to all providers of capital before debt payments (unlevered free cash flow). It answers: what blended return do capital providers require for this risk?

If required returns rise, value falls. If the business gets safer or rates fall, WACC can fall and value rises, all else equal.

Follow-ups you should expect

"Why use after-tax cost of debt?"
Interest tax shield. The government shares part of the cost of debt via deductible interest, so effective cost is Kd(1−t).

"What happens if WACC goes up?"
Present values fall. DCF enterprise value falls. Equity value usually falls if net debt is unchanged.

"What happens if the equity risk premium rises?"
Ke rises, WACC rises, value falls. This is one channel for risk-off markets to hit DCF outputs.

"Current or target capital structure?"
Often target or long-term structure for a going-concern DCF, especially if today's leverage is temporary (post-deal digests, cyclical trough). State your assumption.

"Why not discount UFCF at cost of equity?"
Claim mismatch. UFCF belongs to all capital providers. Discounting it at Ke and calling the output equity value is wrong. Levered cash flows pair with Ke; unlevered cash flows pair with WACC.

"What is a reasonable WACC?"
Depends on sector, country, and rate regime. Have intuition: stable infrastructure-like cash flows sit below speculative software. Do not assert a universal "WACC is always 8%."

"How does more debt affect WACC?"
Mechanically more cheap after-tax debt can lower WACC initially, but Ke rises with leverage because equity gets riskier, and financial distress risk eventually matters. Do not claim debt always lowers WACC forever.

Worked intuition example

Suppose:

• Ke = 10%
• Kd = 6%
• t = 25%
• Target weights: 80% equity, 20% debt

WACC = 0.8 × 10% + 0.2 × 6% × 0.75
     = 8.0% + 0.9%
     = 8.9%

If ERP rises and Ke becomes 11%:

WACC = 0.8 × 11% + 0.9% = 9.7%

In a long-duration DCF, that 80 bps move can change value a lot, which is why interviewers care.

Terminal value warning

In a Gordon growth terminal value:

TV = UFCF_(n+1) / (WACC − g)

If g approaches WACC, terminal value explodes. If someone uses g = 5% with WACC = 6%, be ready to challenge it. This is a classic "does the candidate actually think?" moment.

Common mistakes

How WACC connects to other interview topics

• DCF walkthrough: WACC is the discount-rate step
• EV vs equity: WACC/UFCF → EV; then subtract net debt
• Comps: beta peers and capital structure assumptions often come from the same universe
• Rates / markets question: higher yields can lift Rf and Kd, pressure valuations

Keep those links verbal. Isolated flashcards are how people blank when the interviewer changes topics mid-answer.

Practice plan

Day 1: Deliver the 30-second answer cold
Day 2: Write CAPM and WACC formulas from memory and explain each input
Day 3: Shock Rf, beta, ERP, Kd, tax, and weights; say what happens to WACC and value
Day 4: Build a DCF and sensitize WACC by ±50 bps and ±100 bps
Day 5: Mixed mock: start with "walk me through a DCF," then get interrupted with WACC deep-dives

Numbers make the interview answer feel obvious. If you only memorize definitions, a simple "what if beta is higher?" follow-up will still trip you.