How the CPI is built: 80,000 prices, and shelter sets the pace
Owners' equivalent rent alone is 26% of the index, priced from a rent survey that revisits each unit every six months. Here is what 3.4% is made of.
- What happened
- The August 2026 Consumer Price Index, published on September 11, 2026, put 12-month inflation at 3.4% and core at 2.4%. Shelter, which carried 35.625% of the CPI-U basket at the December 2025 weighting, rose 3.0% over the year; energy, at 6.383% of the basket, rose 16.3%.
- Why
- The CPI is a weighted average of the 80,000 prices the BLS says it collects each month. A third of the weight is shelter, most of it owners' equivalent rent, priced from a rent survey that revisits each unit only every six months. That design makes the largest component the slowest to move.
- The numbers that matter
- 3.4%CPI-U, 12 months to August 2026 (released Sep 11, 2026)35.625%Shelter's share of the CPI-U basket, December 2025 relative importance26.204%Owners' equivalent rent share of the basket, December 202516.3%Energy index, 12 months to August 2026
- Why it matters
- If you own with a fixed mortgage, the biggest line in the index is an imputed rent you do not pay. If you rent, the index describes the average lease, not your renewal. And the Social Security adjustment uses a different index, the CPI-W, which rose 3.5%.
- What happens nextas we saw it on 28 Sep 2026
- The September 2026 CPI is scheduled for Wednesday, October 14, 2026, at 8:30 a.m. ET, according to the BLS release schedule. It completes the third-quarter CPI-W average that sets the Social Security cost-of-living adjustment.
Shelter alone outweighs food, medical care and energy combined; energy cuts across groups (motor fuel sits inside transportation).
| Shelter | 35.6% |
|---|---|
| Transportation | 16.3% |
| Food | 13.7% |
| Medical care | 8.4% |
| Energy | 6.4% |
The 3.4% that the Bureau of Labor Statistics published on September 11, 2026 is not a price. It is an average of the 80,000 or so prices the BLS collects each month, weighted by how a sample of households spent their money in 2024. More than a quarter of that weight is attached to a price nobody pays: the rent that homeowners would charge themselves. Here, from the BLS's own documents, is how the CPI is assembled and why its largest piece moves last.
What the BLS actually prices
In the BLS Handbook of Methods' own rounded figures, prices are collected each month in 75 urban areas from 6,000 housing units and 23,000 retail establishments: department stores, supermarkets, hospitals, gas stations and other stores and service outlets. The CPI Frequently Asked Questions page puts the count of items priced at 80,000 a month. Of the 75 areas, 23 are large enough to represent themselves (21 with populations over 2.5 million, plus Anchorage and Honolulu); the other 52 stand in for the rest of urban America.
Those prices are sorted into 243 item categories and 32 index areas, which the Handbook says yields 7,776 basic indexes. Within most categories the BLS uses a geometric mean, which allows for shoppers buying less of whatever has gone up most; across categories it uses a fixed-weight (modified Laspeyres) formula, which does not.
The CPI-U (all urban consumers) is the index quoted as “inflation”; the Handbook puts its population at 93% of the U.S. total. The CPI-W (urban wage earners and clerical workers) is a subset covering 29%, and the FAQ page confirms it sets the Social Security cost-of-living adjustment through the change in third-quarter averages. In the 12 months to August 2026 the CPI-W rose 3.5%, to an index level of 328.481 (1982–84 = 100), against 3.4% for the CPI-U.
The weights: where the 100 points go
The weights come from the Consumer Expenditure Surveys: the FAQ page describes over 20,000 consumer units interviewed each quarter and 12,000 more keeping spending diaries. Since the January 2023 index the BLS has updated the weights every year, on a lag it describes as 24 months, so the 2026 index uses 2024 spending. The BLS publishes the resulting shares as “relative importance”, and its December 2025 table is the one in force for 2026.
| Component | CPI-U | CPI-W |
|---|---|---|
| Housing | 44.469 | 42.658 |
| of which: Shelter | 35.625 | 33.594 |
| — Rent of primary residence | 7.840 | 10.697 |
| — Owners' equivalent rent of residences | 26.204 | 21.798 |
| Transportation | 16.316 | 18.256 |
| of which: Gasoline (all types) | 2.895 | 3.971 |
| Food | 13.698 | 14.889 |
| Medical care | 8.423 | 7.596 |
| Energy (motor fuel plus household energy) | 6.383 | 8.052 |
| All items less food and energy (“core”) | 79.919 | 77.058 |
Owners' equivalent rent, at 26.204 points, is the single largest line in the index, larger than all of food or all of transportation. The CPI-W leans more on rent, food and gasoline and less on owners' equivalent rent, which is one reason the two indexes drift apart.
The BLS weights page explains that a component's share is its December weight updated by its own price changes, so whatever rises fastest takes a larger slice. Table 1 of the August 2026 release carries a column headed “Relative importance Jul. 2026”: energy stood at 7.347, gasoline at 3.770 (from 2.895 in December) and shelter had slipped to 35.343. The quantities in the basket did not change; the prices did.
How a price nobody pays is measured
Owners' equivalent rent, or OER, exists because the BLS treats a home as shelter, which is consumption, and as an investment, which is not. Its 2022 note on shelter prices states that mortgage interest, property taxes, real estate fees, most maintenance and all improvement costs belong to the capital good and are not consumption items. House prices are not in the CPI, and neither is your mortgage payment. What is in it is an estimate of what your home would rent for.
The BLS factsheet on rent and rental equivalence says owners are asked: “If someone were to rent your home today, how much do you think it would rent for monthly, unfurnished and without utilities?” Those answers set only the weight of OER. The monthly price change comes from the same rent survey that produces the rent index, reweighted toward the kinds of units owners live in (a structure-type factor capped between 0.5 and 2.0) and stripped of utilities bundled into contract rent.
The factsheet states that rent is collected from each sampled unit every six months, because many rents are locked in for a lease term and less frequent collection allows a larger sample. The sample is split into six panels: panel 1 is collected in January and July, panel 2 in February and August, and so on. Each month's index change is the sixth root of the six-month change observed in that month's panel. The BLS's 2022 note adds that over 80% of sampled units have the same tenant as the period before, and many leases run 12 months, so sitting tenants see no price change inside the lease. Private rent measures track vacant units where a landlord sets a new price; the CPI tracks the average lease.
Sitting tenants, 12-month leases and six-month pricing turn the shelter index into a moving average of market rents stretched over a year or more. That is what the average household actually pays, not a flaw. But it means the rental market of months ago is still arriving in the CPI, and because shelter is more than a third of the index, that lag sets the pace of the headline itself.
Seasonal adjustment, headline and core
The BLS publishes two versions of most series. The unadjusted index is the actual price level; the seasonally adjusted one removes recurring patterns from weather, model changeovers, holidays and sales, using the Census Bureau's X-13ARIMA-SEATS software, with factors revised each February. The one-month figure in headlines (+0.4% for August 2026) is seasonally adjusted; the 12-month figure (3.4%) is unadjusted, which the BLS says is the right basis for contracts and escalation.
“Core” is simply all items less food and energy, 79.919% of the CPI-U basket at the December 2025 weighting. The FAQ notes that some users prefer it because food and energy prices are relatively volatile. It is a filter, not a verdict on whether food and fuel matter, and shelter is 45% of it (35.625 ÷ 79.919). See core versus headline.
August 2026, decomposed
The release states that gasoline rose 3.9% in August (seasonally adjusted), “accounting for over one third of the monthly all items increase”, and that shelter rose 0.3% after 0.1% in July. Core rose 0.3% on the month and 2.4% over the year, from 2.5% in the 12 months to July. Over the year airline fares were up 23.4%, motor vehicle insurance down 5.1%, used cars and trucks down 2.3% and new vehicles up 0.6% (Table 1, August 2026 release, September 11, 2026).
Multiply each component's December 2025 relative importance by its 12-month change to August 2026. The three largest movers account for 2.48 of the 3.4 points, leaving 0.92 points for the remaining 44.3% of the basket, consistent with core goods rising only 0.7%. This uses fixed December weights, whereas the BLS's contribution arithmetic tracks weights month by month, so read it as scale, not the official decomposition. Check: 334.980 ÷ 323.976 = 1.0340, the published 3.4%.
| Component | Weight (Dec 2025) | 12-month change | Weight × change | Contribution |
|---|---|---|---|---|
| Shelter | 35.625% | +3.0% | 0.35625 × 3.0 | 1.07 points |
| Energy | 6.383% | +16.3% | 0.06383 × 16.3 | 1.04 points |
| Food | 13.698% | +2.7% | 0.13698 × 2.7 | 0.37 points |
| Three together | 55.706% | 2.48 points | ||
| Everything else | 44.294% | 3.4 − 2.48 | 0.92 points |
At a 35.625% weight, a shelter index running one percentage point faster or slower moves the all-items figure by 0.36 points, all else unchanged. Food would need to move 2.6 points, and energy 5.6 points, to have the same effect.
What it means for your money
If you own with a fixed-rate mortgage, the largest line in the index, 26.204 points of owners' equivalent rent rising 3.1%, describes a cost you are not paying. Your actual shelter cost is the mortgage, which the BLS classifies as a capital cost outside the CPI, plus taxes and maintenance, which it also excludes. Your own inflation rate is weighted differently from the published one; see how a mortgage works and renting versus buying.
If you rent, the 2.7% rent figure averages sitting tenants and new ones. A renewal notice is one new price; the index is the average lease. They answer different questions.
If you receive Social Security, the relevant figure is not 3.4% but the CPI-W, up 3.5% in the 12 months to August 2026, applied through the change in third-quarter averages; the September index, due October 14, 2026, completes that quarter. And a pay rise is compared with inflation by dividing, not subtracting: 4.0% against 3.4% is 1.040 ÷ 1.034 − 1 = 0.6% real. See wages versus prices.
Sources
- Consumer Price Index Summary — August 2026U.S. Bureau of Labor Statistics · Sep 11, 2026 · Primary source
- Table 1. Consumer Price Index for All Urban Consumers (CPI-U): U.S. city average, by expenditure category, August 2026Bureau of Labor Statistics · Sep 28, 2026 · Primary source
- Relative importance of components in the Consumer Price Indexes: U.S. city average, December 2025Bureau of Labor Statistics · Sep 28, 2026 · Primary source
- Relative Importance and Weight Information for the Consumer Price IndexesBureau of Labor Statistics · Sep 28, 2026 · Primary source
- Consumer Price Index Frequently Asked QuestionsBureau of Labor Statistics · Sep 28, 2026 · Primary source
- Handbook of Methods: Consumer Price Index, DesignBureau of Labor Statistics · Sep 28, 2026 · Primary source
- Handbook of Methods: Consumer Price Index, CalculationBureau of Labor Statistics · Sep 28, 2026 · Primary source
- Measuring Price Change in the CPI: Rent and Rental EquivalenceBureau of Labor Statistics · Sep 28, 2026 · Primary source
- Measuring Changes in Shelter Prices in the Consumer Price Index (Commissioner's Corner, May 20, 2022)Bureau of Labor Statistics · Sep 28, 2026 · Primary source
- Seasonal Adjustment Frequently Asked Questions (FAQs), Consumer Price IndexBureau of Labor Statistics · Sep 28, 2026 · Primary source
- Schedule of release dates for principal economic indicatorsU.S. Bureau of Labor Statistics · 2026 · Primary source
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