What Is Marginal Utility?

Marginal utility is the added satisfaction that a consumer gets from having one more unit of a good or service. The concept of marginal utility is used by economists to determine how much of an item consumers are willing to purchase. Positive marginal utility occurs when the consumption of an additional item increases the total utility. On the other hand, negative marginal utility occurs when the consumption of one more unit decreases the overall utility.

Key Takeaways

  • Marginal utility is the added satisfaction a consumer gets from having one more unit of a good or service.
  • The concept of marginal utility is used by economists to determine how much of an item consumers are willing to purchase.
  • The law of diminishing marginal utility is often used to justify progressive taxes.
  • Marginal utility can be positive, zero, or negative.
1:19

Marginal Utility

Understanding Marginal Utility

Economists use the idea of marginal utility to gauge how satisfaction levels affect consumer decisions. Economists have also identified a concept known as the law of diminishing marginal utility. It describes how the first unit of consumption of a good or service carries more utility than later units.

Although marginal utility tends to decrease with consumption, it may or may not ever reach zero depending on the good consumed.

Marginal utility is useful in explaining how consumers make choices to get the most benefit from their limited budgets. In general, people will continue consuming more of a good as long as the marginal utility is greater than the marginal cost. In an efficient market, the price equals the marginal cost. That is why people keep buying more until the marginal utility of consumption falls to the price of the good.

The law of diminishing marginal utility is often used to justify progressive taxes. The idea is that higher taxes cause less loss of utility for someone with a higher income. In this case, everyone gets diminishing marginal utility from money. Suppose that the government must raise $20,000 from each person to pay for its expenses. If the average income is $60,000 before taxes, then the average person would make $40,000 after taxes and have a reasonable standard of living.

However, asking people making only $20,000 to give it all up to the government would be unfair and demand a far greater sacrifice. That is why poll taxes, which require everyone to pay an equal amount, tend to be unpopular. Also, a flat tax without individual exemptions that required everyone to pay the same percentage would impact those with less income more because of marginal utility. Someone making $15,000 per year would be taxed into poverty by a 33% tax, while someone making $60,000 would still have about $40,000.

Types of Marginal Utility

There are multiple kinds of marginal utility. Three of the most common ones are as follows:

Positive Marginal Utility

Positive marginal utility occurs when having more of an item brings additional happiness. Suppose you like eating a slice of cake, but a second slice would bring you some extra joy. Then, your marginal utility from consuming cake is positive.

Zero Marginal Utility

Zero marginal utility is what happens when consuming more of an item brings no extra measure of satisfaction. For example, you might feel fairly full after two slices of cake and wouldn't really feel any better after having a third slice. In this case, your marginal utility from eating cake is zero.

Negative Marginal Utility

Negative marginal utility is where you have too much of an item, so consuming more is actually harmful. For instance, a fourth slice of cake might even make you sick after eating three pieces of cake.

Criticisms of Marginal Utility

The concept of marginal utility was developed by economists who were attempting to explain the economic reality of price, which they believed was driven by a product's utility. However, this led to a problem known as "the paradox of water and diamonds," which is attributed to Adam Smith. It states that water has far less value than diamonds, even though water is vital to human life. Since marginal utility and marginal cost are used to determine price, this is paradoxical because the marginal cost of water is much lower than that of diamonds. Value in use is not the same as value in exchange.

Example of Marginal Utility

David has four gallons of milk, then decides to purchase a fifth gallon. Meanwhile, Kevin has six gallons of milk and likewise chooses to buy an additional gallon. David benefits from not having to go to the store again for a few days, so his marginal utility is still positive. On the other hand, Kevin may have purchased more milk than he can reasonably consume, meaning his marginal utility might be zero.

The chief takeaway from this scenario is that the marginal utility of a buyer who acquires more and more of a product steadily declines. Eventually, there is no additional consumer need for the product in many cases. At that point, the marginal utility of the next unit equals zero and consumption ends.