The CarDependability Index (CDi) turns years of owner-complaint data into an easy-to-understand reliability grade for used cars. Here’s a breakdown of the details:
What the CDi measures
Every grade starts with the problems owners submit to the National Highway Traffic Safety Administration (NHTSA). We then compare that information against sales volume for that year and model, keeping in mind that more popular vehicles may accumulate more complaints than slow-sellers.
We look at two windows: a vehicle’s early years, which drive its letter grade and 0–100 score, and its full lifetime, shown separately as a long-term reliability rate.
Where the data comes from
The CDi is built on public data from NHTSA, the federal agency that collects vehicle safety complaints and recall records. It’s independent: the automakers have no input into the grades and have nothing to do with the CarDependability Index. This approach separates the CDi from opinion-based surveys and impression-focused reviews.
How to read a grade
Each model year earns a letter grade and a 0–100 score. The higher the score, the more dependable.
Alongside the grade, the Long-Term CDi indicates how the vehicle has held up over its full life, with a plain-language band such as “above average” or “well below average.” A car that may have had gremlins in its early years or a relatively trouble-free record may show its true colors over a longer period. A confidence level tells you how much data the grade rests on; vehicles with few complaints on record are graded with lower confidence and flagged accordingly.
What the CDi is and isn’t
The CDi is a model-level overview, not a prediction about one specific car. A strong grade doesn’t guarantee a trouble-free vehicle, and a poor one doesn’t mean every example is bad. Maintenance, mileage, and history also factor in. Our exclusive index reflects problems owners reported, which isn’t the same as every problem that exists. We list recalls separately because these issues are safety-related and not necessarily connected to reliability. Finally, we start compiling the CDi after a model is two to three years old, which usually offers enough time for complaint data to collect.