If you buy an individual stock, you are buying a slice of a business. The income statement is the single page that tells you whether that business actually makes money. It reads top to bottom, and each step subtracts a different kind of cost.
The four lines that matter
- Revenue — everything the company sold. Also called the "top line".
- Gross profit — revenue minus the direct cost of making the product. Tells you how much room the business has to cover everything else.
- Operating profit — gross profit minus salaries, marketing, R&D and administration. This is the profit from actually running the business.
- Net income — what remains after interest and tax. The "bottom line".
Margins beat absolute numbers
A company earning a billion in profit sounds impressive until you learn it took fifty billion of revenue to get there. Divide each profit line by revenue and you get margins, which let you compare a giant to a minnow on equal terms.
Watch the direction more than the level. Margins that are quietly shrinking every year usually mean competition is arriving, and no amount of revenue growth fixes that permanently.
Where the story hides
Two things distort the bottom line more than anything else. The first is one-off items — a lawsuit settlement, a factory sale, a restructuring charge. They belong in the accounts, but they say nothing about next year. The second is interest: a business with heavy debt can have excellent operating profit and thin net income.
Profit is an opinion, cash is a fact. The income statement is where judgement calls live, which is why it should always be read alongside the cash flow statement.
Summary
Read top to bottom, convert to margins, look at three to five years rather than one, and be suspicious of any year where net income looks great but operating profit does not. If a company's profit only appears below the operating line, you are usually looking at accounting rather than a business.