Opportunity cost is the basic concept at the heart of residual income. Opportunity cost refers to what you are giving up to use an asset for a particular project or investment. Let's say you start with $100,000 cash in your stock portfolio and grew that money to $104,000 by spending only a few hours per month trading stocks. Now $4,000 in profit may look just fine when you consider that you only worked, say, 20 hours for it in total. However, once you consider your opportunity cost, your little hobby will not look nearly as profitable. If banks are paying six percent for risk-free certificates of deposit, your $100,000 would have grown to $106,000 simply by depositing it in a bank. Your opportunity cost is $6,000
However, with passive income, there is not a direct connection to time involved. Once the original work is completed, the income continues to come in as long as demand for the product or service exists. Each time a song is downloaded, the musician receives money as a passive income. They did not have to record the song again or do additional work for each download, yet they are paid for their original work.
The second form of residual income, passive income, is often a vital part of wealth creation. There are only so many hours in each day, and when a person trades hours for dollars, there is a maximum amount of income that person can earn. For instance, if a person earns a specific amount each hour, there is a limit to how many hours are available to work. Once they reach that maximum amount of time, they cannot earn more money.
Residual income is the amount of net income generated in excess of the minimum rate of return. Residual income concepts have been used in a number of contexts, including as a measurement of internal corporate performance whereby a company's management team evaluates the return generated relative to the company's minimum required return. Alternatively, in personal finance, residual income is the level of income that an individual has after the deduction of all personal debts and expenses have been paid.