What is Marginal Propensity To Consume (MPC)?

The marginal propensity to consume (MPC) is the proportion of an aggregate raise in pay that a consumer spends on the consumption of goods and services, as opposed to saving it. Marginal propensity to consume is a component of Keynesian macroeconomic theory and is calculated as the change in consumption divided by the change in income. MPC is depicted by a consumption line, which is a sloped line created by plotting change in consumption on the vertical "y" axis and change in income on the horizontal "x" axis.


Marginal Propensity to Consume

BREAKING DOWN Marginal Propensity To Consume (MPC)

The marginal propensity to consume is equal to ΔC / ΔY, where ΔC is change in consumption, and ΔY is change in income. If consumption increases by 80 cents for each additional dollar of income, then MPC is equal to 0.8 / 1 = 0.8.

Given data on household income and household spending, economists can calculate households’ MPC by income level. This calculation is important because MPC is not constant; it varies by income level. Typically, the higher the income, the higher the MPC, because as wealth increases, so does the ability to satisfy needs and wants.

According to Keynesian theory, an increase in production increases consumers’ income, and they will then spend more. If we know what their marginal propensity to consume is, then we can calculate how much an increase in production will affect spending. This additional spending will generate additional production, creating a continuous cycle. The higher the MPC, the higher the multiplier—the more the increase in consumption from the increase in investment.

Example of How Marginal Propensity to Consume Works

Suppose you receive a $500 bonus on top of your normal annual earnings. You suddenly have $500 more in income than you did before. If you decide to spend $400 of this marginal increase in income on a new suit and save the remaining $100, your marginal propensity to consume will be 0.8 ($400 divided by $500).

The other side of marginal propensity to consume is marginal propensity to save, which shows how much a change in income affects levels of saving. Marginal propensity to consume + marginal propensity to save = 1. In the suit example, your marginal propensity to save will be 0.2 ($100 divided by $500).

If you decide to save the entire $500, your marginal propensity to consume will be 0 ($0 divided by 500), and your marginal propensity to save will be 1 ($500 divided by 500).