You buy something, later you sell it for more—you made money. But the tax code doesn’t just tax the money that lands in your bank account. It asks three questions: How much did you really gain? Should that gain appear on this year’s return? And what tax rate applies? This chapter walks through those questions, from the simple math of a single sale to the special rules that can turn ordinary income into lightly taxed capital gain, or let you postpone tax entirely.