The formula and meaning
P/B = Market price per share ÷ Book value per share = Market cap ÷ Total equity (book value). Book value of equity = Total assets − Total liabilities. A P/B of 1.5x means the market pays 50% more than the company's accounting net assets. A P/B of 0.8x means the market prices the equity below book — implying the market believes the company is destroying value or that book value overstates the real worth of assets. The theoretical floor: a company trading below book value might theoretically be worth more liquidated than operated as a going concern.
| P/B level | Typical interpretation | Common examples |
|---|---|---|
| <1x | Market below book — distress or deep value | Banks during crises, declining industrials |
| 1–2x | Near book — stable, capital-intensive | Utilities, insurance, mature industrials |
| 2–5x | Modest premium — reasonable quality | Consumer staples, established financials |
| >10x | Very high — intangibles/franchise value | Software platforms, luxury brands, asset-light |
Why high P/B doesn't mean overvalued
High P/B ratios are justified when a company earns returns on equity (ROE) significantly above its cost of equity. The relationship: P/B = ROE ÷ Cost of equity (for perpetual earnings, no growth). A company earning 25% ROE against a 10% cost of equity should rationally trade at 2.5x book. A company earning only 8% ROE against a 10% cost of equity should trade below book. This ROE-P/B framework — formalised by John Burr Williams and later Penman — explains why "expensive" quality companies often remain justified at high multiples and why "cheap" low-ROE companies deserve to be cheap.
P/B for financial institutions
P/B is the primary valuation tool for banks, insurance companies, and other financial institutions. For banks, "book value" of equity is the regulatory capital that constrains lending capacity — so the ratio represents how much the market values the franchise above its regulatory minimum. A bank trading at 0.5x tangible book is priced as a value trap or turnaround candidate; at 1.5x it is viewed as having a healthy franchise. European banks have persistently traded below book since 2011 due to low ROE, thin margins, and regulatory capital requirements that have compressed returns.
The intangibles distortion
P/B loses much of its meaning for asset-light companies whose true assets — brand, intellectual property, customer relationships, software — are either not capitalised (internally developed intangibles are generally expensed under GAAP/IFRS) or quickly amortised. A pharmaceutical company whose key asset is a drug patent, or a technology company whose key asset is its codebase, may have very little tangible book value relative to its economic value. For these companies, P/B will always appear "high" — not because the stock is overvalued, but because book value is an inadequate proxy for economic asset value.
"A low P/B ratio is a necessary but not sufficient condition for value. The question is always: why is it cheap, and does that reason imply permanent impairment or temporary mispricing?" — Value investing discipline
What this means for you
P/B is most informative in three contexts: comparing financial institutions (where book value = regulatory capital); assessing potential bankruptcy risk (companies at 0.3x book may be pricing in asset impairments); and factor analysis (HML — high book-to-market — is the cornerstone of the value premium). For asset-light businesses, use P/B alongside other metrics: Price/FCF, EV/EBITDA, and return on invested capital are better guides. Always ask whether the accounting book value reflects economic reality before drawing conclusions from P/B.