Which type of financial ratio is calculated using earnings before tax?

The operating margin is the correct choice because it measures the proportion of revenue that remains after covering operating expenses, excluding taxes and interest. This ratio is specifically calculated using earnings before interest and taxes (EBIT), which is reflective of a company's operational efficiency. By focusing on earnings before tax, the operating margin enables investors and analysts to assess how well a company generates profit from its core business operations, disregarding the effects of tax structures and financial leverage.

Other choices are based on different calculations: the net profit margin includes all expenses, including taxes and interest; return on equity assesses profitability in relation to shareholder equity and includes net income, which is derived after taxes; and gross margin measures the difference between sales and the cost of goods sold, focusing only on production costs without overhead or operating expenses. Each of these metrics has its own distinct purpose and approach to evaluating financial performance.