How it works
How Carpool scores a used car
Carpool scores a used car by its cost per remaining mile: the price divided by the miles the car has left. A lower number means more car for your money, and it lets you compare any two cars, whatever their age, mileage or make.
The formula
Cost per remaining mile = price ÷ (expected lifetime miles − current odometer)
Price and mileage come from the listing. Expected lifetime miles come from Carpool's catalog, which holds an estimate for each model family. You can browse the estimates by make.
If you enter a gas price, Carpool adds the fuel cost of each mile as well (gas price ÷ the car's EPA combined MPG), so a thirsty car doesn't look cheaper than it is to run.
Worked examples
Neither the lowest price nor the lowest mileage reliably points to the better buy. These two pairs show why.
| Car | Price | Odometer | Expected life | Miles left | Cost per mile left | Rating |
|---|---|---|---|---|---|---|
| 2014 Toyota Corolla LE | $8,200 | 98,000 | 260,000 | 162,000 | $0.051 | Excellent |
| 2014 Toyota Corolla LE | $6,300 | 222,000 | 260,000 | 38,000 | $0.166 | Good |
| 2011 Toyota Camry LE | $7,500 | 150,000 | 270,000 | 120,000 | $0.063 | Excellent |
| 2015 Chevrolet Cruze LT | $7,500 | 110,000 | 165,000 | 55,000 | $0.136 | Very Good |
The $6,300 Corolla is $1,900 cheaper, but it has 38,000 miles left against 162,000, so every mile costs about 3.3 times as much. The Camry and the Cruze cost the same and the Cruze has fewer miles on it, yet the Camry has the longer road ahead and the lower cost per mile. These are example cars, not real listings.
From score to rating
Each score maps to one of six ratings, from best to worst: Excellent, Very Good, Good, Fair, Below Average, Poor. On Facebook Marketplace, the extension also ranks each car against every other car you've viewed in the last two weeks, across all your searches, so #1 is the best buy you've found so far.
Where the lifetime estimates come from
Lifetime figures are Carpool's own editorial estimates of the odometer miles a well-maintained example typically reaches before major repairs make it uneconomical to keep. They're informed by long-term reliability and high-mileage studies and known powertrain issues. They aren't measured data or a guarantee. Fuel economy comes from EPA vehicle data, and the catalog covers 2000 and newer models.
What the score can't tell you
The score knows the price, the mileage and the model. It doesn't know this particular car's accident history, title status, maintenance or condition. Use it to decide which cars are worth a closer look, then check the history and have a mechanic inspect the car before you buy. A well-kept car can beat its estimate, and a neglected one won't reach it.
Try it
The free extension does this on every car you view on Facebook Marketplace. To score one car by hand, use the car value calculator.
Add to Chrome, it's free