When a news anchor says the economy "grew 3 percent last year," the number behind that sentence is GDP — gross domestic product, the total market value of all final goods and services a country produces in a year. It is the headline scoreboard for the whole economy. One number tries to capture millions of transactions, from haircuts to aircraft.
There are three ways to measure GDP, and the surprising part is that they all give the same answer. The expenditure approach adds up everything people spend: consumption by households, investment by firms, government spending, and net exports. You will see this written as $C + I + G + NX$, where $NX$ is exports minus imports. The income approach adds up everything people earn instead — wages, rent, interest, and profit. The value-added approach sums the value each business adds at every stage, from raw steel to a finished car. Spending equals income equals value added, because one person's spending is always another person's income.
A measure can mislead if prices move. Suppose a country produces the exact same goods this year as last year, but every price doubles. GDP would appear to double even though nothing real changed. To strip out this illusion, economists separate nominal GDP (measured at current prices) from real GDP (measured at constant prices). Real GDP is the honest number, because it counts actual goods, not inflated price tags.
The bridge between the two is the GDP deflator — a price index that captures how much of the change in GDP came from rising prices rather than rising output. Divide nominal by real, multiply by 100, and you get it. If the deflator rose 5 percent, prices across the whole economy rose 5 percent.
GDP is powerful, but it is not the same as well-being. It ignores unpaid work like raising children. It counts pollution cleanup as a gain while ignoring the pollution itself. It says nothing about how income is shared. A country can post a large GDP while most people struggle.
That is why analysts also use the Human Development Index, which blends income with life expectancy and education. A fuller scoreboard than GDP alone, it reminds you that a bigger economy is not automatically a better life.