How the Car Dogs Score is calculated

Step 1: establish what the car cost new

Everything starts from the original transaction price. If you tell us the original MSRP we use it. If you do not, we estimate it from the vehicle's segment (from the federal VIN decoder's body class) and its brand tier: value, mainstream, premium or luxury.

Step 2: apply the depreciation curve

We apply a retention curve by age: roughly 83 percent of original price retained at one year, 75 at two, 68 at three, 62 at four, 56 at five, then flattening toward the low thirties by year ten. Brands with historically strong resale get a 6 percent uplift; brands that historically shed value faster get a 6 percent reduction.

Step 3: adjust for mileage and condition

Expected mileage is 12,000 miles a year times the vehicle's age. Every mile above or below that adjusts value at about 8 cents a mile on a $30,000 car, scaled proportionally for more or less expensive vehicles, and capped at 25 percent of value either way so an outlier odometer cannot produce a nonsense number.

Condition adjusts the result: excellent adds 4 percent, clean is neutral, average subtracts 5 percent, rough subtracts 14 percent.

Step 4: publish the price bands

The result of steps one through three is the fair estimate. Excellent price is 93 percent of it, good price is 97 percent, and anything above 105 percent is flagged as too expensive.

Step 5: score and weight

Each of the six categories is scored 0 to 100, then weighted into the total: price 28 percent, market value 18 percent, mileage 16 percent, history and recalls 14 percent, equipment 12 percent, cost to own 12 percent.

The verdict follows the total: 82 and above is BUY, 55 to 81 is CONSIDER, below 55 is PASS. Our AI writes the explanation, but it is only allowed to explain numbers the math already produced.

What the score cannot do

It cannot see accident history, title brands, owner count, rental or fleet use, or the mechanical condition of the specific car in front of you, because none of that is available from a free public source. It cannot know a dealer's actual cost, and it cannot replace a pre-purchase inspection or a vehicle history report.

Where we do not have data, we say so on the report rather than filling the gap with a guess. That is the whole point.

Our sources

• NHTSA vPIC VIN decoder — Year, make, model, trim, body class, engine, drivetrain and factory safety equipment.
• NHTSA recalls database — Open safety recalls by year, make and model.
• EPA fuel economy data — Combined MPG used in the cost-to-own score and the five-year fuel estimate.
• California DMV fee schedule — Registration, title and value-based fees, plus the state doc-fee cap.