The ratio is calculated from balance-sheet figures reported in SEC filings. Total debt is not always a single reported line. GeminIQ takes it as filed when a company reports it, and otherwise sums short-term and long-term debt, including current maturities, commercial paper, revolving credit, and lease obligations. In XBRL, these components are often tagged DebtCurrent, LongTermDebtNoncurrent, and related elements, and shareholders' equity is usually tagged StockholdersEquity.
Because debt appears in both the numerator and the denominator, the ratio stays bounded and is easier to compare across companies than debt to equity, which can climb into the thousands of percent when equity is small. It is mathematically linked to that ratio: a debt-to-equity figure of 100% corresponds to a debt-to-capital figure of 50%. Some providers include preferred stock and noncontrolling interest in capital, which lowers the result, and the treatment of operating lease liabilities also varies, so check the definition before comparing figures from different sources.
Book equity is the weak point. Companies with large buyback programs or accumulated losses can report negative equity, pushing the ratio above 100% even when the business is healthy. Some analysts use the market value of equity instead, which gives a different and more volatile picture. Credit analysts and rating agencies commonly track debt to capital alongside earnings-based measures such as debt to EBITDA, which show the capacity to repay rather than the funding mix. Banks and insurers are typically assessed with regulatory capital measures instead.