As my wife and I have started to research for our next car purchase, I was introduced to the Rule of 19 by the local car salesman… I asked “Rule of 19?” I am only aware of the Rule of 72.  The car salesman provided the a quick definition being a general rule of thumb of how much your monthly car payment would be for the total amount financed.  The car salesman quickly calculated that for every $1,000 that I financed, I would pay $19 per month. Aware of the car buying process and following the advice of many experts, I wanted to negotiate one thing at a time: #1. Total Car purchase price, #2. Financing (lease vs buy, interest rate), and #3. Trade-in value. Intrigued on what assumptions this rule of 19 depends on, I decided to re-create the math.  Basically, the Rule of 19 is ...