Look up the long-term debt for the company. Long-term debt can be found on the balance sheet or in the notes to the financial statements in the 10K or 10Q. The section will explain how much debt is taken out or issued and the number of years associated with each.
Look up the net income. Net income is usually the last line item on the income statement located in the 10K, 10Q or annual report. Specifically, you want net income after tax.
Divide net income by long-term debt. Let's work through an example. If a company has net income of $10,000 and long-term debt (due over 1 year) of $100,000, then the return on debt = $10,000/$100,000 = .1 or 10 percent.