Macro Note 44
BLS says the expenditure data needed for the final C-CPI-U are not available until 10 to 12 months after the reference month, so the index is first published as a preliminary estimate and later revised. The first print is not the last word.
Why this note matters
Readers can assume a published inflation index is final the moment it hits the release calendar. BLS makes an explicit exception for the chained CPI: the first version is preliminary because the needed expenditure data arrive with a lag.
In its CPI FAQ, BLS says the expenditure data used to compute the final C-CPI-U are not available until 10 to 12 months after the reference month. Because of that lag, BLS says a preliminary estimate of the index is published and later revised.
So unlike the common assumption that a released CPI number is automatically final, the chained CPI arrives in stages.
BLS's CPI technical note says CPI-U and CPI-W are considered final when released, but the C-CPI-U is issued in preliminary form and is subject to three subsequent quarterly revisions. That makes the distinction operational rather than cosmetic.
For readers, the implication is straightforward: a cited chained-CPI value should be understood as revision-prone until BLS has the underlying expenditure data needed for the final version.
Inflation commentary often compresses methodology into a single headline number. BLS's own documentation shows why that can be too casual when the chained CPI enters the discussion.
For Hynexly readers, the practical rule is simple: if someone cites C-CPI-U for a policy or valuation argument, check whether they are relying on a preliminary reading or a later revised version.
BLS explains why final C-CPI-U data lag the reference month and states that preliminary estimates are published first and revised later.
Open sourceBLS explains that CPI-U and CPI-W are final when released, while C-CPI-U is preliminary and subject to later revisions.
Open source