What it means
The index tracks the cost of a fixed basket that includes housing, food, transport, medical care, clothing and recreation. Statisticians collect prices from shops and service providers every month and compare the cost of the basket with a base period.
If the basket costs more than it used to, the index rises. CPI-U is designed to represent urban households, which make up most of the population.
This gives it broad coverage, and it is the version most often reported in the news. A related measure, CPI-W, focuses on urban wage earners and clerical workers and is used for certain benefit adjustments.
Finance teams use the index in many ways. Lease agreements and supply contracts often include escalation clauses that raise payments by the change in the index.
Companies use it to deflate historical revenue figures to see real growth, and treasurers use it to judge whether interest rates are above or below inflation. The index has limits.
It measures an average basket, so a household whose spending is concentrated on rent or fuel may see a different personal inflation rate. It also reflects the quality and mix of goods the statisticians choose, so economists debate how well it captures changes such as new technology or substitution toward cheaper goods.
Because of that, it is wise to treat the index as a benchmark rather than a perfect measure. Where a business wants to protect itself against its own cost increases, it may also track a more specific index, such as a producer price index or a trade-specific cost measure.
Index levels themselves are not as important as changes. A reading of 300 means little on its own; the relevant figure is the percentage change between two dates.
In practice
Real-world examples.
Example
A commercial landlord has a lease with an escalation clause tied to CPI-U. When the index rises 3%, the tenant's rent moves from $5,000 to $5,150 a month. Over a five-year lease the same clause would compound the increases each year.
Example
A retailer's sales rose from $10,000,000 to $10,400,000, which is 4%. With inflation of 3% the real growth is only about 1%, so the board does not celebrate as much as it first planned. Nominal growth is the headline figure, but real growth is what shows whether the business is genuinely larger.
Example
A company agrees a three-year supply contract and includes a clause linking the price to CPI-U. This protects the supplier from rising costs and gives the buyer a predictable formula rather than repeated negotiation. A cap and a floor can be added to limit surprises for both sides.
Formula
Calculation
Inflation rate = ((CPI-U now - CPI-U earlier) / CPI-U earlier) x 100
Suppose the index stood at 300.0 a year ago and is 309.0 now.
Change = 309.0 - 300.0 = 9.0.
Inflation rate = (9.0 / 300.0) x 100 = 3.0%.
A lease with an annual rent of $60,000 that rises with CPI-U would therefore increase by 3.0%, or $60,000 x 0.03 = $1,800, to $61,800. Check: 300.0 x 1.03 = 309.0, which matches the new index level.Case study
Seen in the real world.
Brookside Property Group is an illustrative, fictional landlord with 40 commercial tenants. Its older leases had fixed rents for five years, and when inflation picked up, the cost of maintenance and insurance rose faster than income. The finance director had been surprised how quickly the gap between rents and costs opened.
The finance director revised the standard lease so that rent would be reviewed annually by the change in CPI-U, with a cap of 5% and a floor of 0%. Tenants accepted the cap because it limited their risk, and the landlord accepted the floor because it prevented rent from falling. Legal counsel checked that the new clause named the index, the base month and the calculation method.
In this illustrative case, the new leases kept rental income broadly in line with costs, and the company's net operating income became more predictable. The finance director now reviews the index every quarter alongside the budget. Tenants appreciated the clarity of the formula, and no rent reviews went to dispute in the following two years.
Watch out
Common mistakes.
- Quoting the index level as if it were the inflation rate, rather than calculating the percentage change.
- Assuming CPI-U matches the price changes a specific business or household experiences.
- Using the wrong index in a contract, for example CPI-W in place of CPI-U, which can produce a different result.
Questions
People also ask.
What does the U stand for?
Urban, because the index covers the spending of households living in urban areas. The index covers all urban consumers, which includes most of the population.
How often is the index published?
Monthly, with a publication schedule set by the statistical agency. Contracts should say which month's reading is used.
Can CPI-U be negative?
Yes, the index can fall, which is called deflation, although prolonged declines are unusual.
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