It's 10% towards finance payments over the life of the loan. If you are financing the car over 6 years, multiply our income by 6, then take 10%.
So, if you make 100K and financing over 6 years, you "shouldn't" buy more than 60K car.
that's my math and i'm sticking to it
Everyone's situation is different - finance people have a very narrow goal - save money for retirement. The other end of the spectrum is folks that don't care at all about saving for retirement a "live life now" philosophy. Me...I believe somewhere in the middle is a great place to be.