Every candidate can recite the WACC formula. Almost none could tell me what beta measures, why the weights are at market values, or what happens to the whole number as leverage rises. Those three gaps were where I scored the topic, because the formula is free and the understanding is not. This article is the understanding.
What WACC is, in one breath
WACC in words · the four-line version
WACC is the blended return the company's capital providers require, weighted by the market value of each claim.
It discounts unlevered free cash flows because those flows belong to everyone: the rate must too.
Cost of equity comes from CAPM: the risk-free rate plus beta times the equity risk premium.
Cost of debt enters after tax, because interest is deductible and the state funds part of it.
The second line is the one that matters and it ties this article to its parent: the DCF anchor piece built unlevered flows precisely so that this blended rate is the matching denominator. Rate and flows must describe the same investors, always.
The components, one honest sentence each
- Risk-free rate. A long government bond yield, matched to the currency and horizon of the cash flows. Matching matters more than the level and the level itself belongs to your market view, which the macro article on this site keeps current so this one does not have to.
- Beta. The sensitivity of the stock to the overall market: how much systematic, undiversifiable risk the business carries. It is the only company-specific input in the cost of equity, which is why the follow-ups concentrate on it.
- Equity risk premium. The extra return equity investors demand over the risk-free rate, taken from long-run historical or implied estimates. It is a convention with a range and saying exactly that, a convention with a range, reads as honesty rather than ignorance.
- After-tax cost of debt. The company's borrowing rate times one minus the tax rate. The tax shield is why debt is the cheaper instrument and the seed of the best follow-up in the topic, below.
The two follow-ups that separate candidates
First: why market-value weights rather than book? Because WACC is a forward-looking required return and investors require returns on what their claims are worth today, not on what accountants recorded years ago. Book weights would discount tomorrow's cash flows at a rate built from history.
Second, the big one: what happens to WACC as the company adds debt? The lazy answer, WACC falls because debt is cheaper, fails. The real shape is a shallow U: at first, cheap after-tax debt pulls the average down, but rising leverage makes both the equity riskier, beta and the cost of equity climb and eventually the debt itself more expensive as distress risk appears. Past some point the average turns back up. A candidate who can sketch that trade-off in three sentences has demonstrated more finance than most of the formula-reciters in the pile combined.
Beta relevering, in three lines
Peer betas · why we unlever and relever
Take betas from comparable listed companies, but their betas carry their capital structures.
Unlever each one, stripping out the leverage effect, to get the risk of the business alone.
Average, then relever at the target's own structure. The result prices the business you are valuing, financed the way it is actually financed.
This is the standard practitioner's method and a frequent modelling-test step; being able to say why each line exists, rather than just performing it, is the difference the examiners are listening for.
The fumbles I saw every season
Reciting CAPM and freezing on 'what does beta mean'. Book-value weights, offered confidently. 'More debt always lowers WACC', which invites the distress question the candidate then cannot answer. And false precision: defending a discount rate to two decimals when the honest treatment is a range, sensitised, which is exactly how it feeds the terminal value mechanics in the next article of this series. Hold WACC as a reasoned range and every downstream number inherits the honesty.
One rehearsal that works: explain this entire article aloud to someone outside finance in five minutes. If they follow it, you understand it. If you want the follow-ups run at full interview pressure instead, that is the IBD Recruiting Review.
FAQ
What is WACC and why is it the DCF discount rate?
The blended return all capital providers require, weighted at market values. Unlevered cash flows belong to everyone, so the discount rate must too.
What happens to WACC as a company adds debt?
A shallow U: cheap after-tax debt pulls the average down first, then rising equity risk and eventual distress costs turn it back up. More debt does not always lower WACC.
Why do you unlever and relever beta?
Peer betas carry peer capital structures. Stripping leverage isolates business risk; relevering at the target's structure prices the business as it is actually financed.
Former Executive Director in TMT Investment Banking at Nomura and M&A banker at BNP Paribas. Top-rated mentor with 300+ sessions. About
