To determine your car's trade-in value online, visit reputable automotive websites like Kelley Blue Book, Edmunds, or AutoTrader. Input your vehicle's details, including make, model, year, mileage, and condition, to receive an instant estimate. These platforms use advanced algorithms considering market trends and regional factors to provide accurate valuations. Additionally, some websites offer tools that allow you to compare trade-in offers from various dealerships. Keep in mind that the final trade-in value may vary based on the physical inspection of your car by the dealer. Always provide honest information for the most accurate estimate.