The simple version

Most big government numbers arrive as a first estimate and move later, as the count fills out. People have learned to expect that.

The main price measure is the exception. The figure published on release day is the final one, and it does not get recalculated when more information turns up.

There is a catch, and it is not the one people expect. A smoothed version is published alongside the raw one, and that smoothed version is rebuilt every year and reaches five years into the past.

The numbers

• The Bureau of Labor Statistics states in its CPI technical note that the CPI-U and CPI-W are considered final when released, while the chained measure, the C-CPI-U, is issued in preliminary form and subject to three subsequent quarterly revisions.
• Seasonally adjusted data are a separate matter. The same note says the seasonal factors are updated each February, and that the new factors are used to revise the previous 5 years of seasonally adjusted data.
• The note states the window directly as well: seasonally adjusted data, including the US city average all items index levels, are subject to revision for up to 5 years after their original release.
• Past that window the door shuts. The note says seasonally adjusted indexes beyond the last 5 years of data are considered to be final and not subject to revision.
• There is a dated instance in the note. For January 2026, revised seasonal factors and seasonally adjusted indexes for 2021 to 2025 were calculated and published.
• The note also records that for the seasonal factors introduced for January 2026, BLS adjusted 57 series using intervention analysis seasonal adjustment, including selected food and beverage items, motor fuels and vehicles.
• The agency draws a practical conclusion from its own policy. The note says BLS advises against the use of seasonally adjusted data in escalation agreements because seasonally adjusted series are revised annually for five years.
• The note states that the unadjusted data are of primary interest to consumers concerned about the prices they actually pay, and that unadjusted data are also used extensively for escalation purposes.
• On timing, the published release schedule lists the October 2026 reference month for November 10, 2026 at 8:30 AM, and the January 2027 reference month for February 11, 2027.

Three different ways a number can change

The first way is the one everybody knows. A count goes out before all the answers are in, and later answers move it. That is how the employment and growth figures behave.

The second way is nothing of the kind. The raw price figure stays exactly where it was, and only the smoothing method on top of it is rebuilt, which changes the month-to-month pattern without anyone collecting a single new price.

The third way is that nothing changes, ever, which is the raw figure itself. Three mechanisms, one phrase covering all of them, and treating them as the same thing is how people end up surprised by a past that moved.

The actual math on a five-year rewrite

Five years of monthly data is 60 separate monthly figures. That is the span the note says gets recalculated when the new factors arrive.

So in one go, 60 published monthly readings of the smoothed series can be restated. The instance the note names is the set for 2021 through 2025, recalculated for January 2026.

Nothing underneath those 60 figures changed. The prices collected in any one of those months are the same prices. Only the arithmetic sitting on top of them was redone.

What this means

If you are comparing a month-over-month price change you wrote down last year against the same month today, check which version you have. The smoothed one may not match itself across time.

It also explains a choice that looks arbitrary from outside. Contracts that move payments with prices use the unadjusted series, and the agency's own note gives the reason: the adjusted one gets revised.

What this is NOT

This article explains which parts of the Consumer Price Index get revised and which do not, using the Bureau of Labor Statistics CPI technical note as its only source, read on November 9, 2026. It is not a forecast of any inflation reading, not a view on whether the index is measured correctly, and not a claim about any figure in any particular monthly release, including the October 2026 release that the published schedule places on November 10, 2026 and which did not exist when this was written. It does not tell anyone which series to use in an agreement: where that comes up, the article reports what the agency itself advises and nothing more, and anyone drafting a contract should take that to a professional rather than to this page. The only arithmetic of ours is that five years of monthly data is 60 monthly figures. The note uses both framings of the annual update, saying the factors are updated each February while describing the set introduced for January 2026, and this article reports both rather than reconciling them. This is not a political endorsement or criticism of anyone.

Sources

• US Bureau of Labor Statistics, CPI News Release Technical Note, read November 9, 2026, for the final-when-released statement, the February factor update, the five-year revision window, the January 2026 instance, the 57 intervention-analysis series, and the escalation guidance.
• US Bureau of Labor Statistics, Schedule of Releases for the Consumer Price Index, read November 9, 2026, for the October 2026 and January 2027 reference-month release dates.