CPI calculator: percent change in the index between two months

Choose an area and two months: the result is the change in the published CPI-U, with both index levels and the series code to check them on bls.gov.

U.S. average, a metro area, a region or a city-size class

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CPI-U change, U.S. average

+3.7 %

September 2025 to September 2026, base 1982-84=100.

Start index324.8
End index336.94
Change in index points12.14
Percent change+3.74 %
BLS seriesCUUR0000SA0
How this is computed

Prepared by Radif Partners · How the figures are built · BLS indexes through September 2026

The CPI-U for the U.S. city average stood at 336.94 in September 2026 and 324.8 a year earlier, a change of 3.7 %: that is the 12-month inflation rate the BLS reported on October 14, 2026. A CPI calculator does nothing more than divide one index by another, but it has to pick the right two numbers: the right area, the right month and the version not seasonally adjusted, which is the one used in contracts and never revised. This one reads the values from the BLS files for the national index, the 4 regions, the 2 size classes and the 23 metro areas. It shows both levels, the change in index points and the series code (CUUR0000SA0 for the national index), so you can check them on the BLS data pages. If you already have two index values, from a lease or an older publication, the advanced options take them as typed. Months the BLS did not price, including October 2025 everywhere, are labeled and replaced by the nearest earlier month, never estimated.

Index points and percent change

The CPI is an index, not a price. In the U.S. city average, 100 is the average level of 1982-84, and 336.94 in September 2026 means prices are 237 % higher than then. Between two months the index can move by a few points; what matters for a raise or a contract is the percent change, the ratio of the two levels minus one. From January 2020 to September 2026, the national index rose from 257.971 to 336.94, a change of 78.969 points and 30.6 %.

A point change is the same everywhere only in appearance. Each local index has its own base, and some do not use 1982-84 at all (Phoenix is based on December 2001, Riverside on December 2017), so 5 points in one area and 5 points in another do not mean the same percentage. The calculator always reports the percentage.

Which month, which area

The New York index is published every month and rose 4.5 % over the 12 months to September 2026. Boston is priced in odd months only: a request for August 2026 in Boston uses July 2026, and the result says so. Twenty of the 23 metros work this way, half in odd months and half in even months. The regions and the national index are monthly.

Change in the New York CPI over 12 months

CPI-U change, New York

+4.5 %

Start index348.096
End index363.87
Change in index points15.774
Percent change+4.53 %
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Two months deserve a warning. October 2025 does not exist: during the lapse in appropriations the BLS collected no prices, published a dash with the footnote "Data unavailable due to the 2025 lapse in appropriations", and will publish no 12-month change for October 2026. And the latest month of the year has no annual average yet: the average of 2026 will be published with the December index, on January 13, 2027.

Typing your own index values

Older leases quote an index level that does not match today's tables, for instance on the old base 1967 = 100, which the BLS still publishes for some series. Open the advanced options, type the two levels, and the calculator gives the change between them without looking anything up. Both must be on the same base; mixing a 1967 base with a 1982-84 base gives a meaningless ratio.

Seasonally adjusted or not

The BLS publishes each index twice for the nation. The seasonally adjusted series removes the regular pattern of the year (heating in winter, clothing sales in January) and is the one used for month-to-month headlines. It is revised for five years. The not seasonally adjusted series is final at publication, and its 12-month changes are the ones the BLS reports as the annual rate. Contracts and escalation clauses almost always name the not seasonally adjusted CPI-U, which is the only version this calculator uses. Local indexes are published only not seasonally adjusted.

Checking a figure on bls.gov

Every result carries its series code: CUUR, then the area code (0000 for the nation, S12A for New York, S11A for Boston), then SA0 for all items. Type it into the BLS data finder or the series report to see the same values. The method page lists every code the site uses and the tests it runs against the BLS release; the CPI by city page lists all the areas with their latest month.

One last habit worth keeping: write down the series code and the two months you used next to the result. When the question comes back a year later, at the next renewal or the next raise, you can redo the calculation in seconds with the same series, instead of starting from a figure nobody can trace.

For the value of an amount rather than a percentage, use the inflation calculator; for a whole year at a time, the inflation rate by year table; for the three national measures side by side, the CPI-U, CPI-W and chained CPI page.

Questions people ask

How do I calculate the percent change in the CPI?

Divide the later index by the earlier one, subtract 1 and multiply by 100. With the CPI-U, use the version not seasonally adjusted for both months and the same area. The calculator does it for you and shows both index levels, so you can check them against the BLS tables or the clause of a contract.

What is the current CPI index value?

336.94 for the U.S. city average CPI-U in September 2026, not seasonally adjusted, on the base 1982-84 = 100. The same month a year earlier was 324.8. Local indexes have their own levels; New York was at 363.87 the same month.

Can I use the CPI calculator with an index from an old lease?

Yes, as long as both values are on the same base. Open the advanced options and type the start and end index levels; the calculator uses them as given and ignores the BLS files. If the lease names the 1967 base, compare it with the 1967-based value for the later month, not with a 1982-84 value.

Why does the calculator change my month?

Because the area you chose was not priced that month. Twenty metro areas are published every other month, and no area has an index for October 2025. The calculator uses the latest earlier month that exists and writes which one under the result; it never invents a value between two published months.

Keep going

Inflation calculator

Inflation rate by year

U.S. inflation for every year since 1914, annual average and December to December, plus any metro or region.

CPI by city

The 23 metro areas the BLS publishes, their rhythm, latest month and 12-month inflation, side by side.

CPI-U vs CPI-W vs chained CPI

The three national price indexes on the same amount: who they cover, who uses them, how far apart they drift.

October 2025 CPI

The month the BLS never published, why, and what it changes for calculators, contracts and the 2026 figures.

Official sources for this page

Prepared by

Independent publisher of inflation calculators built month by month from the CPI-U indexes of the 23 metro areas, 4 regions and 2 city-size classes

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Results apply the published CPI indexes to the amount you type. An index tracks the average prices paid by urban consumers in an area, not your own budget, and it does not compare price levels between cities. A month the BLS did not publish is never filled in: the calculator names the index it uses instead.

Indexes through September 2026, BLS files read on