Marginal Propensity to Save (MPS)

A marginal propensity to save refers to the proportion of an aggregate raise in pay that a consumer spends on saving rather than on the consumption of goods and services. The marginal propensity to save is a component of Keynesian macroeconomic theory and is calculated as the change in savings divided by the change in income.

Marginal propensity to save = change in saving / change in income

MPS is depicted by a savings line: a sloped line created by plotting change in savings on the vertical y axis and change in income on the horizontal X axis.

Suppose you receive a $500 bonus with your paycheck. You suddenly have $500 more in income than you did before. If you decide to spend $400 of this marginal increase on a new business suit and save the remaining $100, your marginal propensity to save is 0.2 ($100 change in saving divided by $500 change in income). The other side of marginal propensity to save is marginal propensity to consume, which shows how much a change in income affects purchasing levels. Marginal propensity to consume + marginal propensity to save = 1. In this example where you spent $400 of your $500 bonus, marginal propensity to consume is 0.8 ($400 divided by $500). Adding MPS (0.2) to MPC (0.8) equals 1.

Given data on household income and household saving, economists can calculate households’ MPS by income level. This calculation is important because MPS is not constant; it varies by income level. Typically, the higher the income, the higher the MPS, because as wealth increases, so does the ability to satisfy needs and wants, and so each additional dollar is less likely to go toward additional spending. However, the possibility remains that a consumer might alter savings and consumption habits with an increase in pay.

Naturally, with an increase in salary comes the ability to cover household expenses more easily, allowing for more leeway to save. With a higher salary also comes access to goods and services that require greater expenditures. This may include the procurement of higher-end or luxury vehicles or relocation to a new, pricier residence. If economists know what consumers’ MPS is, they can determine how increases in production will influence saving.

MPS is also used to calculate the expenditures multiplier using the formula 1/MPS. The expenditures multiplier tells us how changes in consumers’ marginal propensity to save influence production. The smaller the MPS, the larger the multiplier.