Understanding Marginal Propensity to Save
When households receive an increase in disposable income—whether through wage rises, tax cuts, or bonuses—they face a choice: spend it or save it. The marginal propensity to save (MPS) quantifies this behaviour by measuring the proportion of each additional dollar that goes into savings.
MPS ranges from 0 to 1. An MPS of 0.3 means households save 30 cents of every extra dollar earned, spending the remaining 70 cents. An MPS of 0 indicates all additional income is spent; an MPS of 1 indicates all additional income is saved. MPS is the inverse of marginal propensity to consume (MPC): if MPC = 0.7, then MPS = 0.3.
This metric matters because it influences the money multiplier—a key mechanism through which income changes ripple through the economy. Higher MPS reduces the multiplier effect; lower MPS amplifies it.
The MPS Formula
Marginal propensity to save is calculated by dividing the change in consumer savings by the change in disposable income. You can also derive MPS by subtracting the marginal propensity to consume from 1.
MPS = Δs ÷ Δyd
MPS = 1 − MPC
Δs— Change in household savings (in currency units)Δyd— Change in disposable income (in currency units)MPC— Marginal propensity to consume (fraction between 0 and 1)
Real-World Example
Suppose a family's disposable income rises by £2,000 annually. Over the same period, their savings increase by £500. Using the formula:
MPS = £500 ÷ £2,000 = 0.25
This household saves 25% of additional income and spends 75%, meaning their MPC = 0.75. This is typical for middle-income families in developed economies, where MPS typically ranges from 0.1 to 0.4 depending on age, wealth, and economic conditions.
The Paradox of Thrift
Individual savings are financially prudent, yet when the entire population increases their MPS simultaneously, the economy can contract—a counterintuitive phenomenon called the paradox of thrift. When MPS rises economy-wide, aggregate consumption falls, reducing business revenue and employment. Lower incomes then reduce total savings, negating the intended benefit.
This paradox illustrates why macroeconomic outcomes depend on collective behaviour, not just individual rationality. During recessions, central banks and governments often encourage spending (lowering MPS) to prevent this deflationary spiral, even though personal saving seems prudent in isolation.
Key Considerations When Using MPS
MPS varies significantly across demographic groups and economic conditions; understanding these nuances improves interpretation of results.
- MPS changes with income level — Lower-income households typically have higher MPC and lower MPS because they allocate most additional income to essential consumption. Wealthier households show higher MPS because their basic needs are already met, allowing them to save more discretionary income.
- Economic conditions shift savings behaviour — During recessions or uncertainty, households raise their MPS as a precaution, even without income growth. Conversely, optimistic periods lower MPS as consumers spend more freely. The calculator reflects a snapshot; trends matter more than single-period values.
- MPS excludes non-income wealth changes — The formula measures response to income changes only. If households increase savings due to asset price changes or inheritances rather than income growth, traditional MPS calculations miss this behaviour and may be misleading.
- Cultural and institutional factors influence MPS — Pension systems, social safety nets, and cultural attitudes toward saving vary globally. Two countries with identical income distributions may exhibit very different MPS values due to these structural differences.