In this guide, I'll teach you about the 20/4/10 rule and how it can be applied to financing a car. I will then go on to showing you how to setup an Excel sheet to apply that rule to your finances. It will include one table that uses the rule to tell you the price of a car you can afford, and what you should use for the down payment. Then there will be a separate table that will take in the price of a car, and show you what the car payment would be. You should use Excel for this, so you can follow along with the steps, but a similar program would work. Just know that the exact steps may not apply.