CPI-U, CPI-W and chained CPI-U: the same prices, three answers
Choose an amount and a starting December: the three national measures of the BLS carry it to today side by side.
December 2015 to September 2026
$1,425 (CPI-U)
CPI-W gives $1,433, the chained CPI-U $1,386.
| CPI-U | +42.5 % |
| CPI-W | +43.3 % |
| Chained CPI-U | +38.6 % |
| CPI-U minus chained | 3.9 points |
The chained CPI-U is preliminary for its last 10 to 12 months and is revised; CPI-U and CPI-W are final.
Prepared by Radif Partners · How the figures are built · BLS indexes through September 2026
The BLS publishes three national consumer price indexes from the same prices. The CPI-U covers over 90 percent of the population, all urban consumers, and is the one quoted as "the" inflation rate: 3.7 % over the 12 months to September 2026. The CPI-W covers about 30 percent, households of wage earners and clerical workers, gives more weight to transportation and energy (8.1 % of its basket against 6.4 % for the CPI-U), and drives the Social Security COLA; it rose 3.9 % over the same 12 months. The chained CPI-U uses the CPI-U population but lets the weights follow what households substitute when relative prices change; it has been used since 2017 to index federal tax brackets, and its last 10 to 12 months are preliminary. From December 2015 to September 2026, $1,000 becomes $1,425 with the CPI-U, $1,433 with the CPI-W and $1,386 with the chained CPI-U.
Same prices, different households
All three indexes start from the prices that BLS collectors record in 75 urban areas. What differs is whose spending decides how much each price counts. The CPI-U represents all urban households: households in core-based statistical areas and in urban places of 10,000 people or more, which is over 90 percent of the population. People in rural areas outside metro areas, on farms, on military bases and in institutions are outside it.
The CPI-W is a subset. It counts households where at least one member worked 37 weeks or more in the past year in a clerical, sales, service, laborer or construction occupation, and where at least half of the household income comes from such work. That is about 30 percent of the population, and retirees are mostly outside it. Its basket leans toward the car and the gas pump: transportation is 18.3 % of the CPI-W against 16.3 % of the CPI-U, and medical care 7.6 % against 8.4 % (December 2025 weights).
The chained CPI-U, or C-CPI-U, uses the same population as the CPI-U. Its difference is the formula. The CPI-U and CPI-W keep the weights of one year fixed for twelve months; since January 2023 data, those weights are updated every year from a single calendar year of spending. The final chained index uses a superlative formula with monthly spending, so when the price of one category jumps and households buy less of it, its weight falls. The BLS notes that some consider it a closer approximation to a cost-of-living index.
| CPI-U | CPI-W | Chained CPI-U | |
|---|---|---|---|
| Population | over 90 % of U.S. | about 30 % | same as CPI-U |
| Weights | fixed 12 months, updated yearly | fixed 12 months, updated yearly | monthly, follow substitution |
| Revised? | no (not seasonally adjusted) | no (not seasonally adjusted) | yes, for 10 to 12 months |
| Areas | U.S., regions, 23 metros | U.S., regions, 23 metros | U.S. only |
| Main uses | headline rate, most contracts | Social Security COLA | federal tax brackets (since 2017) |
| Base | 1982-84 = 100 | 1982-84 = 100 | December 1999 = 100 |
How far apart they drift
Over a month the three indexes rarely differ by more than a few tenths. Over years the gap adds up. From December 2000 to September 2026, the CPI-U rose 93.6 % and the chained CPI-U 82.0 %, about 0.25 percentage point a year apart. Earlier BLS evidence put the gap at around 0.2 point a year. It is not a law: the chained index can rise faster in a given month, as it did in January 2023.
The three measures since a December of your choice
December 2010 to September 2026
$1,537 (CPI-U)
| CPI-U | +53.7 % |
| CPI-W | +53.6 % |
| Chained CPI-U | +48.1 % |
| CPI-U minus chained | 5.7 points |
The CPI-W usually sits close to the CPI-U, above it when gasoline climbs and below it when gasoline falls, because of its heavier weight on transportation and energy. In September 2026, with energy up 20.4 % over a year, the CPI-W 12-month change was 3.9 % against 3.7 % for the CPI-U.
Which one to use
A contract or a lease. Use what the document names. If it says "the CPI" without more, it almost always means the CPI-U, U.S. city average, all items, not seasonally adjusted. A document that names the CPI-W or the chained CPI-U means that index and no other; the chained one is awkward in a contract because its recent values are revised.
Social Security and federal benefits. The law ties the Social Security COLA to the CPI-W, through the average of July, August and September. The COLA page lists every adjustment since 1975 and rebuilds those since 1984, when the third-quarter rule began, from that index.
Taxes. Since 2017 the inflation adjustment of federal income tax brackets uses the chained CPI-U. Because it rises a little more slowly, brackets widen a little more slowly than they would with the CPI-U.
Your own budget. None of them is your basket. A retiree who drives little and spends more on medical care, or a renter in a city where rents rose fast, has an inflation of their own. The spending group calculator lets you apply the index of one group to your own spending.
The revision trap of the chained index
The chained CPI-U is published first as a preliminary estimate, because the spending data it needs arrive 10 to 12 months late. The latest month in the file here is September 2026, and the months of the past year will change when the BLS publishes final values. The CPI-U and CPI-W not seasonally adjusted are never revised once published. If you compute a figure with the chained index today, write down the date: the same calculation next year can give a slightly different answer. The 2025 final values are affected by the missing October and November 2025 spending data; the BLS adjusted the weights and plans the final October to December 2025 figures for November 10, 2026.