September CPI, due October 14: the 324.800 base and what BLS publishes

A year ago the September CPI did not come out on schedule. The Bureau of Labor Statistics published the September 2025 figures on Friday, October 24, 2025, after a lapse in appropriations shut most of the agency, and it produced that one release so that the Social Security Administration could meet its statutory deadlines. The notice rescheduling it, dated October 10, 2025, said no other releases would be produced until regular government services resumed. That is a reminder of what the September CPI is for: it is the release on which the following year's benefit checks are calculated.

In 2026 the release is on the calendar as normal. The BLS October 2026 schedule lists the Consumer Price Index for September 2026 at 8:30 a.m. Eastern Time on Wednesday, October 14, 2026, alongside Real Earnings for the same month. This piece is not a forecast and contains no expected figure. It sets out what BLS publishes on that morning, what the arithmetic of the 12-month rate looks like given the index levels already on record, and which household numbers are built from it.

What is published at 8:30 a.m.

The news release is a text summary followed by a fixed set of tables. The August 2026 release, published on September 11, 2026, is the template: the September one has the same structure with the months shifted along by one.

Two columns in Table 1 do most of the work. The unadjusted index columns give the level of the index for the same month a year earlier, the previous month and the reference month, on the 1982–84 = 100 base. The seasonally adjusted percent change columns give the month-on-month moves for the latest three months. The 12-month figure that makes the headline is computed from the unadjusted levels; the monthly figure that makes the headline is the seasonally adjusted one. They answer different questions, and the release says so.

The difference is not academic. In the September 2025 release, gasoline rose 4.1% on a seasonally adjusted basis but 1.1% before seasonal adjustment. Same month, same pump prices, two published figures three percentage points apart, because gasoline normally falls in September and the adjustment removes the usual seasonal decline.

A reader who wants a figure that will not change later should therefore read the unadjusted columns. A reader who wants to know whether prices accelerated in September relative to August should read the seasonally adjusted ones, and accept that the figure may be revised in February 2027.

The base: 323.976 becomes 324.800

The 12-month rate is a ratio of two index levels. The August 2026 release put the all items CPI-U at 334.980, against 323.976 in August 2025, which is where the 3.4% came from. On October 14 the denominator changes to the September 2025 level, which the archived September 2025 release gives as 324.800.

Because the base is already known, it is possible to say what level of the September 2026 index corresponds to any given 12-month rate, and what monthly unadjusted move from August that level would represent. The table below is arithmetic on the published base, not a view on which row is likely.

How precise the number is

That error bar is worth keeping beside the headline. A monthly print that differs from the previous one by 0.1 percentage point is inside the range the agency itself attaches to the estimate. The site's piece on how the CPI is built goes through the sampling in more detail; this one does not repeat it.

Two populations, two indexes

The release publishes two headline indexes. The CPI-U covers all urban consumers, which the BLS questions-and-answers page says constitutes over 90% of the US population. The CPI-W covers urban wage earners and clerical workers, approximately 30% of the population. In August 2026 the CPI-W stood at 328.481, up 3.5% over 12 months, a tenth above the CPI-U figure.

The CPI-W is the one that matters for Social Security. The BLS page states that the cost-of-living adjustment is defined as the percent increase between third-quarter averages of the CPI-W, and that BLS does not set how other agencies use it. The third quarter is July, August and September. July and August 2026 are already published; the September figure on October 14 is the third and final input. The site's COLA article walks through that average with the two months already in hand, so it is not repeated here.

The I bond inflation rate uses the CPI-U instead, and uses the unadjusted index over a six-month window ending in September, as the I bond formula article sets out. The September 2026 index level is the end-point of that window. Both numbers, the COLA and the I bond rate, are therefore fixed by levels in Table 1 on October 14 rather than by the percentage in the headline.

What it means for your money

For a household the September CPI is less a verdict on inflation than a set of inputs to things that are paid. The mechanism is the same in each case: a published index level goes into a formula that someone else has already written down.

• Social Security and SSI benefits. The 2027 adjustment is the third-quarter 2026 average of the CPI-W divided by the third-quarter 2025 average. The September 2026 CPI-W completes the numerator. The Social Security Administration announces the result; BLS supplies the index.
• I bonds. The inflation component of the rate for bonds bought from November 2026 is set from the March-to-September 2026 change in the unadjusted CPI-U. A reader who holds I bonds can recompute it from Table 1 on the morning of October 14.
• Escalation clauses. Leases, pensions and union contracts tied to the CPI almost always reference the unadjusted index, which is final when published. The seasonally adjusted figure in the headline is not the one in those contracts.
• Real wages. The Real Earnings release for September 2026 is scheduled for the same morning at 8:30 a.m. It divides average hourly earnings by the CPI-W, so a reader can see on one day whether September pay kept pace with September prices. Nominal versus real is the distinction that release exists to make.

None of this requires knowing the September figure in advance. It requires knowing which column to read when it arrives: the unadjusted index level in Table 1 for anything that is paid, and the seasonally adjusted monthly change in Table A for anything that is argued about.

The calendar after October 14

The schedule is published by BLS a year ahead and is the place to check whether a figure being quoted is the latest one that exists. The site's release calendar mirrors it, and the guide to checking whether a number is current explains the two-dates habit that makes the CPI easy to read correctly.