How the US car-insurance price index is built

The series

The headline series is CUUR0000SETE: the consumer price index for motor vehicle insurance, US city average, not seasonally adjusted, on a 1982-84=100 base. We hold 773 monthly readings, from March 1947 to June 2026.

A second series, CUUR0000SA0, is the all-items index for the same population. It is used in one place only: restating an old statutory minimum limit at today’s price level on the state requirements pages. It never touches a premium figure.

How the change is computed

The twelve-month change for a month is the index for that month divided by the index twelve months earlier, less one. Nothing is smoothed, chained or annualised. Where the year-ago month is missing from the series the change is not computable, and the page says so rather than showing a zero.

Re-basing an amount works the same way: the amount multiplied by the later index and divided by the earlier one. The arithmetic runs in cents and rounds once, at the end.

The check that has to pass

The Bureau publishes both the index levels and its own percent changes. That makes an unusually strong test available: recompute the changes from the levels and require them to match what the Bureau printed. This site does that on every build, and refuses to build if any month disagrees.

The months that are missing

2 months are absent from the series: October 2025 and November 2025. The Bureau did not publish them because of the lapse in appropriations. We do not interpolate across a gap, because an interpolated index level is not a published statistic and would silently become the base for a later twelve-month change.

What this index is not

It is not an average premium and has no dollar level. It is not a forecast. It is not specific to any state, any driver or any coverage level, and it cannot be combined with the filed sample rates elsewhere on this site — those are levels for defined hypothetical drivers in one state, and this is a national rate of change.

What a price index measures, in more detail · How the rest of the site is built

Questions

Why use an index rather than an average premium?

An average premium mixes price changes with changes in what people buy, where they live and what they drive. An index holds the basket constant and measures price alone. It is the only figure in this subject that is comparable month to month.

Does the index tell me what I will pay?

No, and no tool on this site will tell you that. The index describes the direction of prices across US urban consumers. Restating your own premium at another month’s index level says what the index did over that period, not what your insurer will charge.

Seasonally adjusted or not?

The series published on this site is the not-seasonally-adjusted one, CUUR0000SETE. The Bureau revises its seasonally adjusted series each January; the not-seasonally-adjusted series is not revised, which is what makes it safe to hold as a dated record.