Return on Equity

The numerator is net income attributable to common shareholders, which means net income after tax, after minority interest, and after preferred dividends have been deducted. The denominator should match that claim: common shareholders' equity, excluding preferred stock and excluding non-controlling interests reported within equity under both IFRS and US GAAP. Mismatching the two, for instance dividing consolidated net income including minority interest by parent-only equity, inflates the ratio mechanically.

Because equity is measured at a point in time while earnings accumulate across the period, the standard convention averages beginning and ending balances. Averaging matters most where equity moved sharply during the year through a large issuance, a major repurchase, an impairment, or an acquisition settled in shares. Where interim balances are available, a multi-period average reduces the distortion further.

The three-part decomposition rewrites return on equity as net profit margin multiplied by total asset turnover multiplied by the equity multiplier, where the multiplier is average total assets divided by average equity. Read left to right, this separates how much profit each sales dollar produces, how much revenue each asset dollar generates, and how much the asset base is financed by borrowing rather than owners' capital.

The five-part version splits the margin further into a tax burden, an interest burden, and an operating margin. Tax burden is net income over pre-tax income; interest burden is pre-tax income over earnings before interest and taxes; operating margin is EBIT over revenue. This exposes the trade-off inside leverage: additional debt raises the equity multiplier but depresses the interest burden ratio, so incremental borrowing only lifts return on equity while the return on assets exceeds the after-tax cost of debt.

Shareholders' equity is a book figure shaped by accounting history, not an economic measure of capital at risk. Large accumulated repurchases carried in treasury stock, goodwill written off in a prior impairment, restructuring charges, and accumulated other comprehensive income losses all shrink the denominator and lift the ratio without any improvement in operations. Firms with heavy internally generated intangibles expense that investment immediately, leaving thin book equity and structurally elevated returns relative to asset-heavy peers.

Sign problems also arise. When equity turns negative after sustained buybacks or deficits, the ratio becomes meaningless and should be reported as not meaningful rather than as a negative percentage. Two loss-making periods can likewise produce a positive-looking figure when both numerator and denominator are negative.

Return on equity is the engine of the sustainable growth rate, calculated as the retention ratio multiplied by return on equity, where the retention ratio equals one minus the dividend payout ratio. That product estimates how fast a firm can expand equity, and therefore earnings, without issuing new shares or changing its capital structure. It feeds directly into terminal growth assumptions in dividend discount models.

The same input drives the justified price-to-book multiple, expressed as return on equity minus growth, divided by required return on equity minus growth. A firm earning exactly its cost of equity justifies a multiple of one; the premium above book value comes from the spread between the two. Candidates should be able to move fluently between the ratio, its DuPont components, and these valuation identities, and to explain which component changed when the reported figure moves.