There are no tricks. What is going to happen is that you already owe more than the car is worth right now and you will be "upside-down" on your loan. Say you owe $23,000 on the car still and the trade in value is $18,000, you are going to owe the dealership the extra $5,000 ON TOP of the cost of the SUV. Now the easiest way to figure a car payment is take the first 3 digits of the cost (plus any extra like the $5,000) and multiply them by 2 and your payment will be close to that. Say the SUV is $30,000, the other amount is $5,000 for a total of $35,000. Now take 350x2 and $700/month will be close to what the payment will be. You WILL NOT keep your payment close to the same no matter what due to the balance of the loan. Now if its more than 1/2 paid off then it MIGHT work in your favor.