How the price index measures car insurance

What the index measures

The motor vehicle insurance index is one item inside the Consumer Price Index for All Urban Consumers. This site tracks the not seasonally adjusted series, CUUR0000SETE, whose base period is 1982-84=100, meaning the index reads one hundred for the average of those base years. The published series begins in March 1947 and now runs to 773 monthly observations.

Price collectors working for the statistical agency gather premiums for a fixed sample of policies and re-price the same coverage for the same insured characteristics each period. When a policy’s coverage or the insured risk changes, the change is adjusted for, so that the index reflects price movement rather than a change in what was bought. That discipline is what makes the series a price measure at all.

A price index is not an average premium

The index has no dollar units. At June 2026 it reads 858.481, which means only that the same coverage costs that many times its base-period price, divided by one hundred. It cannot be converted into what anybody pays, and no reading of it identifies a typical premium.

What it does support is a ratio. Dividing one month’s index by another’s gives the price change between them, which is the arithmetic behind the re-basing tool on this site: a premium at one date, expressed at another date’s index level. The output describes the index, not the reader’s policy, and the tool says so on its face.

Relative importance and the headline rate

Every item in the basket carries a relative importance: its share of consumer spending, published by the statistical agency and updated annually. Motor vehicle insurance is a small share of the all-items index, CUUR0000SA0, which this site also tracks for the real-terms figures on the requirement pages of all 51 jurisdictions, including the 38 where no regulator publishes premium data at all.

A small weight has a large consequence for interpretation. A dramatic move in car insurance prices moves headline inflation only slightly, so the item can be the sharpest mover in the basket while barely showing in the number reported on the news. Readers who feel a change that the headline does not reflect are not imagining it; they are reading a weighted average of everything else.

Seasonal adjustment and revision

The agency publishes both a seasonally adjusted and a not seasonally adjusted version of the series. Seasonal adjustment removes recurring within-year patterns so that consecutive months can be compared; it is the right series for asking what happened last month. The unadjusted series is the right one for a twelve-month change, because comparing a month with the same month a year earlier already removes the seasonal pattern.

The two differ in one more respect that matters for a reference site: the seasonally adjusted series is revised each January as new factors are calculated, while the unadjusted series is not revised. This site publishes the unadjusted series so that a figure cited here does not silently change months later.

The release calendar and two missing months

Releases follow a fixed calendar published a year ahead, and this site tracks twelve scheduled release events across a year, each one re-stamping the index pages. The next covers July 2026 and is scheduled for 2026-08-12.

The series also has a hole in it. Exactly 2 months are missing: October 2025 and November 2025. Price collection was suspended during the 2025 lapse in appropriations and those months were never published afterwards, because prices cannot be collected retrospectively. No twelve-month change can be computed against a missing month, and this site reads the series across the gap rather than through it, showing the gap rather than interpolating over it.

Questions

Does the index say what car insurance costs?

No. It has no dollar units. At June 2026 it reads 858.481 against a base of 1982-84=100, which describes price change relative to that base period and nothing about any individual premium.

Why are two months missing from the series?

Price collection was suspended during the 2025 lapse in appropriations, so October 2025 and November 2025 were never published. Prices cannot be collected after the fact, which is why the gap is permanent rather than filled in later.

Why use the unadjusted series rather than the adjusted one?

Because the unadjusted series is not revised, while the seasonally adjusted one is recalculated each January. A figure cited from the unadjusted series stays as published.