Base Years and Chained Real GDP

To measure real GDP, you value every year's output using a fixed set of prices from some base year. That lets you compare quantities across time without inflation muddying the picture. But picking one year's prices and freezing them means the weights you use to add up apples, cars, and laptops stay stuck in that year's relative values. If laptops have gotten dramatically cheaper relative to everything else since the base year, a growth calculation using old prices will overweight laptop production, because back then laptops were expensive and counted heavily. That makes measured growth drift away from what actually happened to production.

Chaining fixes this by never letting prices get stale. Instead of comparing every year back to one fixed base year, chained GDP compares each year only to the year right next to it, using prices that are close in time and therefore still relevant. Those year-to-year growth rates get linked together, like links in a chain, to build a continuous series. This keeps the weighting current and avoids the upward distortion that a decades-old base year creates, especially for fast-changing sectors like electronics.

This matters for telling inflation measures apart too. The GDP deflator is not just the CPI under another name. The CPI tracks a fixed basket of goods a typical urban household buys, including imports, and prices that basket every month. The GDP deflator covers everything produced domestically, and its basket changes every period because it is built from current output, not a fixed list. That is why the two indexes usually move together but are not identical, and why the deflator fits naturally into chained real GDP: both update their weights as the economy itself changes.