Definition Definition

Marginal Rate of Substitution: Formula of Marginal Rate of Substitution with Example

What is Marginal Rate of Substitution?

Marginal Rate of Substitution (MRS) typically examines the link between two identical items and is a frequent statistic in economic research. The MRS is the number of components of one product that a customer is ready to abandon in return for components of another product while remaining equally happy. 

It is used to evaluate buyer behavior in an indifferent concept. MRS is crucial in current consumer decision-making theory because it assesses comparative marginal value.

Understanding Marginal Rate of Substitution

At optimum levels of spending, marginal resources consumed rates are identical as well as are computed between product packages with graphs. The MRS in economics indifference concept assesses an item's capacity to replace other comparable goods in direct proportion to changes between goods. 

Whenever economic rules of diminishing marginal returns impact market volatility, the graph's curve seems to have a negative gradient, indicating that customers prefer one commodity over another. 

An indifference slope can be used to depict a comparison of two individual objects that provide customers with equivalent value and contentment. The marginal rate of substitution is founded on the concept that modifications in two replacement items do not affect weight.

The fundamental downside to the MRS approach is that the theory only corresponds to two components at a period. It also does not compensate for the elements that determine the influence on goods usages, such as technology, cheaper price ranges, or fewer skills. 

A further disadvantage of the MRS would be that it believes the marginal benefit of both items will be indifferent, even if two goods may have different usage levels among customers.


MRSxy​∣=dx / dy​=MUy /Mux



  • X and Y indicate two distinct commodities
  • d’y / d’x = derivative of y concerning x
  • MU denotes the marginal utility of two commodities, namely good Y and good X.

Practical Example

A customer, for instance, must pick between sandwiches and pizzas. To assess the effective exchange rate, the customer is questioned about which sandwich and pizza choices produce the same degree of pleasure.


Good X

Good Y







One can figure out from the following table where points A and B denote the customer's willingness to swap two pizza units for one extra unit of sandwiches. As a result, the customer's MRS of X for Y is two during this point.

In Sentences

  • The MRS is a critical computation in the understanding of indifference curves.
  • MRS incorporates constrained reasoning, wherein customers make buying habits to meet their requirements rather than just to find the best alternative.
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