Interviewers love asking about beta because it's easy to compute but exposes a subtle conceptual gap: most candidates know the CAPM formula, but far fewer understand why beta needs to be unlevered and relevered before it can be used at all. This article explains what unlevered beta actually measures, why the adjustment matters, and how the Hamada equation ties it together.

What Beta Measures

Beta measures how sensitive a stock's returns are to movements in the overall market. A beta of 1.0 means the stock moves in line with the market; a beta above 1.0 means it's more volatile, and below 1.0 means it's less volatile. The beta you pull from a data provider (Bloomberg, CapIQ, or a regression against historical returns) is the company's levered beta — it reflects both the risk of the underlying business and the risk added by that company's specific use of debt.

That second part is the problem. Debt adds financial risk on top of business risk: fixed interest payments make earnings to equity holders more volatile, especially when times are tough. Two companies in the exact same industry, with the exact same operating risk, can have very different levered betas simply because one carries more debt than the other.

Why You Need to Unlever Beta

If you're building a valuation and pulling beta from comparable companies, this is a real problem — you're not trying to capture how those companies happen to be financed, you want to isolate the risk of the underlying business (the "asset risk") so you can then apply it to the capital structure of the company you're actually valuing.

The fix is to strip the financing effect out of each comparable company's beta — this is called unlevering — and then rebuild ("relever") a beta at the target company's own debt-to-equity ratio. This two-step process is exactly what's demonstrated with real numbers in Case 11: Calculating Unlevered Beta and Adjusting for a Private Company, where a private company's beta has to be built entirely from public comparables.

The Hamada Equation

The Hamada equation is the standard tool for moving between levered and unlevered beta. To unlever:

βU = βL / [1 + (1 - T) × (D/E)]

Where βL is the levered (observed) beta, T is the tax rate, and D/E is the company's debt-to-equity ratio. Dividing by a term greater than 1 always pulls the beta down — makes sense, since you're removing the extra risk contributed by leverage.

To relever at a new capital structure, you run the formula in reverse:

βL(new) = βU × [1 + (1 - T) × (D/E)new]

This is the formula that lets you take a beta built from unlevered, asset-risk-only comparables and apply it to whatever capital structure you actually care about — whether that's a private company with no traded beta of its own, or the same company at a different leverage assumption.

Why This Matters Beyond the Formula

The unlever/relever mechanic isn't just an academic exercise — it directly feeds into cost of equity (via CAPM) and therefore WACC, which in turn is the discount rate in a DCF. Get the relevering step wrong and every downstream valuation number is wrong too. It also explains a result that surprises a lot of candidates: increasing leverage doesn't automatically increase WACC, because a higher (relevered) beta pushes cost of equity up, but the shift toward cheaper, tax-advantaged debt can offset it. Case 42: WACC with Leverage walks through this exact scenario with a full before-and-after comparison, building on the mechanics introduced in Case 36: WACC: The Building Blocks.

Common Confusion Points

Two mistakes come up constantly in interviews. First, candidates unlever using the wrong tax rate — always use the comparable company's own tax rate to unlever its beta, and the target company's tax rate to relever. Second, candidates forget that at D/E = 0, unlevered and levered beta are identical by definition, since there's no leverage to strip out in the first place.