Knowing income statement real well is critical to your investing success. Income Statement is crucial in determining the fair value of a common stock. Why? Because I believe that the fair value of any investment is determined by the return it can generate for a given price. If a common stock is trading at $ 100 and it earns $ 4 annually, then it is yielding 4%. If a treasury bond is yielding 5% right now, who would want to buy a common stock which yields only 4%? To be honest, there are probably some investors out there who will buy stocks at any price. However, this type of investing is seldom profitable.

Analyzing income statement will tell us how much profits a company can earn. This will in turn tell us how much percentage return we can expect. So, without further ado, let us go through the components of a typical income statement.

Revenue. Also called sales, Revenue is the lifeblood of a company. To earn revenue, a company has to sell. For retail companies like Walmart, you have to sell items at the stores. For service companies such as H&R Block, it has to sell its expertise to tax filers.

Cost of Revenue. Sometimes called Cost of Good Sold, Cost Revenue is the direct cost of providing a particular good or service to customers. For example, the cost of selling one can of soda at Walmart is the price it bought the soda from manufacturers.

Gross Profit This is the difference between the price of good or service that a firm sells and the cost of providing that particular good or service. In other words, it is the mark up that a firm impose on its customers. For example, if Walmart sells a can of soda for $ 1.00 while it costs $ 0.60 from the manufacturer, then gross profit of Walmart for selling that can of soda is $ 0.40. When gross profit is expressed in term of percentage, it is called gross profit margin. In this case, gross profit margin of Walmart is ($0.40/ $ 1.00) x 100% = 40%.

Research & Development.This is the cost of doing research in order to provide future revenue or cost improvement. Either way, it is designed to boost the firm's future profit. For example, Walmart may spend certain dollars in order to improve its inventory management, which in turn will reduce cost of operating its business.

Selling General & Administrative. This is a really broad category. Basically, this is the fixed cost of doing business. Marketing expense, office rent, manager and the CEO's salary is included here. So do depreciation and amortization expense. For your information, depreciation expense is the expense incurred every year for buying a long-term assets such as machinery or vehicle. Amortization expense is the expense incurred for obtaining goodwill, which is obtained from acquiring companies above its net asset value. When a company is considering layoffs, it is this cost that they are trying to reduce.

Operating Income. This is the difference between gross profit and operating expenses. Operating expense here is the total cost of research development and selling general & administrative. Operating income can be thought as the income generated as a result of a firm's primary business activities.

Other Income/Expense. This is the income earned or expense incurred outside of the firm's business activities. For example, capital gain on sale of asset or expense incurred due to lawsuit punitive damage.

Interest Expense. This is the expense incurred from borrowing long term debt. A firm gets additional funding by borrowing money. In turn, it has to pay interest for the loan. This interest is called interest expense.

Income Before Tax, Income Tax Expense. Once you take out all the other income/expense and interest expense from operating income, you get income before tax. A profitable firm has to pay tax on this income. The tax paid by the firm is found in the income statement under category income tax expense.

Net Income. This is our final destination. This is the reason why we go through all the components of an income statement. Also known as net profit, net income is what a company earns at a specific time frame. From here on, you can then calculate the fair value of the firm. Does it yield less than 4% treasury bond, which is considered safe haven? If so, the common stock definitely needs to be sold or avoided.

Please note that each companies have different ways of presenting their income statements. However, most companies present them similar to the above criteria. If some companies give a totally different ways of presenting their financial performance, it is best to ask them questions or avoid the common stock altogether.