Total And Marginal Utility

You can gain insight into the answers to these questions by understanding marginal utility, especially the marginal utility of money.

Utility is the satisfaction that a person derives from the consumption of a good or service. Total utility is the total satisfaction received from consuming a given total quantity of a good or service, while marginal utility is the satisfaction gained from consuming another quantity of a good or service. Sometimes, economists like to subdivide utility into individual units that they call utils. However, because utility is subjective, meaning that it differs from person to person, and because it varies continuously, depending on the quantity consumed, an util cannot actually be measured, but is simply a heuristic device that allows economists to talk about the degree of satisfaction of a product or service.

Although one definition of utility is usefulness, usefulness is not a quality in economic utility. For instance, water is very useful, but doesn't have much utility for most people. On the other hand, judging by recent gold prices in the market, gold has great utility for some people, but it is not very useful.

One quality of marginal utility is that it always declines for each successive quantity consumed of a particular good. If you like ice cream, and you eat one scoop, the first scoop will provide the greatest satisfaction. If you eat another scoop, you'll probably enjoy that also, but the satisfaction will be less than for the first. At some point, you will not want any more ice cream. The marginal utility will drop to zero and will even become negative. This is an everyday illustration of the law of diminishing marginal utility. Marginal utility declines for everything, including money. Although many people want to amass great wealth, each dollar that is accumulated becomes worth less and less, because the marginal utility of what it can buy declines.

Quantity Marginal
Total Utility Curve
Marginal Utility Curve

Declining marginal utility explains why the demand curve slopes downward as the supply quantity is increased, and why people will only consume more if the price declines, since people's willingness to pay also declines.

Marginal utility can also be related to the elasticity of demand. If demand is inelastic, then the quantity demanded drops off slowly as the price increases, indicating that the marginal utility of the product or service is high; with elastic demand, quantity drops off sharply, indicating that the marginal utility of the product is low, so the consumer is not willing to pay a higher price.

Consumer Choice

Consumer choice is guided by preferences for specific products, budget constraints, prices, and the marginal utility of products. A budget constraint exists because the consumer only has so much money, so he can only spend so much; therefore, even among things that he desires, he must still make a choice. This choice will depend on the marginal utility of the product and its price. Because marginal utility declines with quantity, while the price does not vary, a consumer will tend to buy as much product until the marginal utility of the product falls below the marginal utility of other products that the consumer can buy. Hence, the consumer stops buying more of a product when the marginal utility of an additional amount is less than its price. In this way, the total utility of what the consumer can purchase within his budget is maximized. So the marginal utility of each type of product divided by its price will be roughly equal to the marginal utility of the other products that the consumer purchased divided by their prices.

Marginal Utility of Product A
Price of Product A
=Marginal Utility of Product B
Price of Product B

Indifference Curve Analysis

How consumer choice varies with marginal utility is sometimes depicted with indifference curves. Each point on an indifference curve represents a combination of products that yields the same total utility for the consumer. Because each consumer's purchasing power is limited, this budget constraint, represented by a budget line, limits the choices that the consumer can actually make.

Indifference curve analysis is simplified by assuming that the consumer spends all of her money on 2 products. For instance, suppose the consumer has $12 to spend on cantaloupes and apples. Each cantaloupe costs $2 apiece and each apple costs $1 apiece. The following table shows what can be purchased:

Apples Cantaloupes

This yields the following budget line:

Consumer Budget Line

An indifference curve for this example would yield every combination of apples and cantaloupes that yield the same total utility. Indifference curves are convex to the origin because of the law of diminishing marginal utility — when there is a predominance of cantaloupes, then the marginal utility of an additional cantaloupe is less than the marginal utility of an additional apple, and vice versa. In other words, consumers like variety. A tangent line to an indifference curve represents the marginal rate of substitution (MRS) of one product for the other that maintains total utility.

Diagram showing the consumer's maximum utility where the budget line is tangent to the highest utility indifference curve.

An indifference map can be created by several indifference curves representing an increased budget for apples and cantaloupes that allows the consumer to buy more of each product for a greater total utility. Generally, consumers with higher incomes will have larger budgets for specific items. In the above diagram, for instance, I1 represents the indifference curve at the lowest total utility of the 3 displayed in the diagram. The consumer would not choose any point on this curve because her higher income with her correspondingly increased budget for cantaloupes and apples would allow her to achieve greater total utility by choosing a point on indifference curve I2 that would still be affordable. When the consumer's budget line is superimposed on the indifference map, the point where the budget line is tangent to the highest indifference curve is the highest attainable total utility, given the consumer's budget, and represents the consumer's equilibrium position. Although curve I3 offers higher utility, the price of any combination of cantaloupes and apples on this indifference curve is outside of her budget.

Explaining the Real World Using Marginal Utility

The marginal utility of goods and services directly affects the marginal utility of money, for if the additional value of goods and services falls, so does the money used to buy those items. Marginal utility explains a lot in our economy, including the answers to the questions posed at the beginning of this article.

Why do investors fear loss more than desire gain? Investors are more fearful of losing a certain amount of money than their desire to gain the same amount of money, if the probability of the gain or loss is equal. So if someone has $100,000 to invest, where the investment will yield, with a 50% probability per option, either a $50,000 gain or $50,000 loss, most investors, especially risk-averse investors, would forgo the investment, because the loss of the $50,000 has more value — greater marginal utility — than the gain of an additional $50,000. Of course, if the gain had a greater probability, then the investor will be more likely to invest. How much more likely would depend on the perceived probability of the gain or loss and on the risk profile of the investor.

The desire for higher income drops off significantly after $75,000 because the marginal utility of money declines significantly. In most locations, it is a sufficient income to pay for a decent living, which is why other things become more important, such as time off.

A painting is just an array of colors on a canvas, earns no income, costs money to store and insure it, so the only hope for profit is if someone else will pay even more for it later. So why would someone pay $100 million for a painting? Obviously, someone rich enough to afford the finest things in life, so the marginal utility of the $100 million to the buyer is small, so if the investment results in a loss, then it is not a loss that would have much consequence for the buyer. After all, no one would spend $100 million for a painting if that is all they had! It also explains why rich people pay $35,000 for a purse or over $1 million for car. Of course, many rich people like to show off their wealth; it is how the rich measure themselves among themselves — it represents their status. For someone who only has $35,000, they certainly would not use it to buy a purse, since many other things will have much greater marginal utility, including food, shelter, healthcare, and so on.

The poor person needs the money to buy essential goods and services: food, shelter, health insurance, and so on, and even the whole $20,000 would not cover it. On the other hand, the rich person earning $1 million annually still has $100,000 after paying the 90% tax, which still allows her to buy all of these essential necessities of life. If she only paid the 20% rate that the poor person paid, then she could buy a nicer house, a nicer car, and so on, but the improvement would have declining marginal utility. Although I cannot quantify the marginal utility in these cases, it's not unreasonable to assume that the poor person paying a 20% rate has a much greater tax burden than the rich person paying the 90% rate, because the rich person can still live well, even if not as well as she could if she paid the 20% rate.

The above are not complete explanations, but marginal utility does provide insight into the economic behavior of people.