While residual income can be used to describe the amount of net income after all costs are paid down, it also refers to the amount of money you continue to generate after your initial work is done. There are countless ways to make money, but some are much more time-intensive than others. Active income, for example, refers to when you directly act or perform a service for money, including salaries, wages, tips, commissions, and income from a business you’re actively involved with.

In equity valuation, residual income represents an economic earnings stream and valuation method for estimating the intrinsic value of a company's common stock. The residual income valuation model values a company as the sum of book value and the present value of expected future residual income. Residual income attempts to measure economic profit, which is the profit remaining after the deduction of opportunity costs for all sources of capital.