In real life, economists use complex mathematical models to predict what consumers hypothetically would pay for something. The rate of that increase is constant as long as y is fixed (second derivative). Or, you could think about marginal utility, the utility I'm getting from the next incremental chocolate bar or the next incremental pound of fruit. There are 15 references cited in this article, which can be found at the bottom of the page. It represents the "profit" in terms of utility the consumer gets from buying each product. As a general rule, MU is equal to the change in total utility divided by the change in the quantity of goods consumed. Thanks. And before I move on, there's one thing-- and this was a point of confusion for me when I first learned this-- is OK, I'm using the word marginal utility … {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/4\/44\/Calculate-Marginal-Utility-Step-1-Version-3.jpg\/v4-460px-Calculate-Marginal-Utility-Step-1-Version-3.jpg","bigUrl":"\/images\/thumb\/4\/44\/Calculate-Marginal-Utility-Step-1-Version-3.jpg\/aid2032673-v4-728px-Calculate-Marginal-Utility-Step-1-Version-3.jpg","smallWidth":460,"smallHeight":345,"bigWidth":728,"bigHeight":546,"licensing":"