Method
New price = old price × (index at the comparison month ÷ index at the base month), unless a floor or a cap replaces the raw percent. Both index levels must come from the same series. CPI-U all-items U.S. city average is CUUR0000SA0, base 1982–84=100, not seasonally adjusted. CPI-W all-items is CWUR0000SA0. Garbage and trash collection is CUUR0000SEHG02, base December 1983=100.
The documented national example, September 2025 to September 2026: 336.940 ÷ 324.800 = 1.037377, or 3.738%. On $3,000 with a 2% floor and a 5% cap, the collar does not bind, and the price is $3,112.13. The same months for garbage and trash collection, 686.972 ÷ 652.831, are 5.230%. A 4% cap on that series would bind. Using the all-items headline on a trash clause is the wrong bill.
This is one adjustment step. Clauses that compound say the percent applies to the fee then in effect, so you run a step per year and round as the contract requires. Clauses that use the original-base method always divide today's index by the original month's index and apply it to the original price. Do not do both.
Publication lag: the index for a month is released the following month. A September index is not available in September. Bimonthly cities never publish the off months. Phoenix is on a December 2001=100 base, Riverside on December 2017=100, Tampa on 1987=100. Different bases are another reason not to mix series.
Employment Cost Index clauses are not computed here. ECI is quarterly and is not CPI. If the contract says ECI, stop and use the ECI release it names.
Questions
Why not use the CPI percent from the news?
The news percent is one 12-month window, rounded, for one series. Your clause names its own series and its own months. From September 2025 to September 2026, CPI-U U.S. city average moved from 324.800 to 336.940, which is 3.738%. A clause with a 3% cap bills 3%. A clause that names the trash-collection index bills a different percent entirely.
Do you use seasonally adjusted CPI?
No. Commercial clauses use the not-seasonally-adjusted index unless they explicitly say otherwise. Seasonally adjusted indexes are revised. This calculator only offers unadjusted series.
How are the cap and the floor applied?
The raw change is the index ratio minus one. If that change is below the floor, the floor replaces it. If it is above the cap, the cap replaces it. The price is then the old price times one plus the applied change, rounded half-up to the cent. This is one step, not a multi-year compound. For compounding, run the anniversary steps in order, using each year's output as the next year's price.
What if my metro does not publish the month in the contract?
Bimonthly metros publish every other month. Dallas-Fort Worth publishes odd months. Houston publishes even months. Do not average the neighboring months unless the clause tells you to. If the clause is silent, the month is unavailable and the finding should say that.
Index ratio · CPI-U · Cap · Floor · Metro tables · Machine-readable levels
Sources and limits
Index levels from the U.S. Bureau of Labor Statistics Consumer Price Index, not seasonally adjusted, retrieved through the BLS Public Data API on November 1, 2026. Values are index points, not the headline 12-month percent.
Statewide rates reflect U.S. Department of Labor state minimum-wage postings as updated January 1, 2026, the U.S. Department of State Diplomatic Note on 2026 increases, and, for the prior-year comparison and named local rates, the National Employment Law Project compilation published in November 2025. Confirm the rate that applies to the workplace before using it in a bill.
The contracts in these worksheets are fictional. The prices are chosen so the arithmetic is easy to check. They are not a price survey and they are not client results.
RateClause is not a law firm. Nothing on this page is legal advice. Your clause controls, including whether a past period can be rebilled at all.
Primary postings: BLS Consumer Price Index, U.S. Department of Labor, state minimum wages, U.S. Department of State notice of 2026 minimum-wage increases.