Gap insurance covers the difference between your car's actual cash value and your loan balance if the car is totaled or stolen. You can note the general formula as:
Gap Insurance = Loan Balance - ACV
For example, if you buy a car for $20,000 and it’s valued at $15,000 when lost, with a $1,000 deductible, gap insurance will pay for the $5,000, while your collision or comprehensive coverage will cover the $15,000. Your primary insurance would cover the ACV, leaving you with just the deductible to pay. Without gap insurance, you would have to pay the full amount of your loan even if you no longer have your car.