MPC Calculator - Marginal Propensity to Consume
Enter the change in disposable income and the change in consumer spending to calculate the Marginal Propensity to Consume (MPC). The calculator also computes the Marginal Propensity to Save (MPS), the spending multiplier, and the full Keynesian consumption function. Switch to Consumption Function mode to project total consumer spending from any income level.
What is the Marginal Propensity to Consume?
The Marginal Propensity to Consume (MPC) measures how much of every additional dollar of disposable income a household or economy spends on consumption rather than saving. It is defined as the ratio of the change in consumer spending to the change in disposable income: MPC = Change in Consumption / Change in Disposable Income. Because households can only spend or save additional income, MPC always lies between 0 and 1, and MPC + MPS = 1, where MPS is the Marginal Propensity to Save. A household with an MPC of 0.8 spends 80 cents of each new dollar and saves 20 cents.
The consumption function and how to use it
Keynes formalised the relationship between income and spending as the consumption function: C = a + MPC x Yd, where C is total consumer spending, a is autonomous spending (the minimum level of consumption that happens regardless of income, funded by savings, credit or transfers), and Yd is disposable income. Enter your known MPC in Consumption Function mode, add autonomous spending, and change the disposable income slider to see how projected spending and savings shift. This is the same equation used in national income accounting and fiscal policy modelling.
The spending multiplier and why it matters
The spending multiplier (also called the Keynesian multiplier or fiscal multiplier) measures the total increase in economic output generated by each additional dollar of new spending. It equals 1 / (1 - MPC) = 1 / MPS. With an MPC of 0.8, the multiplier is 1 / 0.2 = 5, meaning a $1 billion injection of government spending theoretically generates $5 billion of total GDP over successive rounds of spending and re-spending. In practice, leakages such as taxation, imports, and precautionary saving reduce the real-world multiplier below its theoretical maximum, but the concept still underpins fiscal stimulus arguments worldwide.
MPC vs. APC: what is the difference?
The Average Propensity to Consume (APC) is total consumer spending divided by total disposable income (C / Yd), while MPC measures only what happens at the margin, meaning with a small extra increment of income. APC can exceed 1 for low-income households that spend more than they earn, while MPC is theoretically capped at 1. Economists use MPC for marginal analysis and multiplier calculations, and APC to describe the overall consumption pattern of a household or economy. Both appear in this calculator: APC is shown in the results panel once you enter an income level.
MPC ranges and economic interpretation
| MPC range | MPS range | Spending multiplier | Interpretation |
|---|---|---|---|
| 0.00 - 0.30 | 0.70 - 1.00 | 1.4x - 1.0x | Very high saving, small multiplier |
| 0.30 - 0.50 | 0.50 - 0.70 | 2.0x - 1.4x | Moderate saving |
| 0.50 - 0.70 | 0.30 - 0.50 | 3.3x - 2.0x | Moderate consumption |
| 0.70 - 0.85 | 0.15 - 0.30 | 6.7x - 3.3x | High consumption, significant multiplier |
| 0.85 - 1.00 | 0.00 - 0.15 | Very large | Very low saving, large multiplier effect |
Standard ranges used in Keynesian economics. MPC always falls between 0 (all saved) and 1 (all spent). MPS + MPC = 1 by definition.
Frequently asked questions
What is the formula for MPC?
MPC = Change in Consumer Spending / Change in Disposable Income, often written as MPC = delta-C / delta-Yd. For example, if income rises by $2,000 and spending rises by $1,600, MPC = 1,600 / 2,000 = 0.80.
How do MPC and MPS relate to each other?
They are complements that always sum to 1: MPS = 1 - MPC. Every additional dollar of disposable income is either spent (MPC) or saved (MPS). If MPC is 0.75, then MPS is 0.25, meaning 75 cents is consumed and 25 cents is saved from each new dollar.
What is the spending multiplier, and how is it calculated?
The spending multiplier (Keynesian multiplier) equals 1 / (1 - MPC), which is the same as 1 / MPS. It represents the total increase in GDP per dollar of new autonomous spending as each round of spending becomes someone else's income. A higher MPC produces a larger multiplier: MPC 0.9 gives a multiplier of 10, while MPC 0.5 gives a multiplier of 2.
Can MPC be greater than 1?
Theoretically, MPC is always between 0 and 1 for an individual household, because you cannot spend more than you receive from a single income increment without depleting savings. In macroeconomic data it can occasionally exceed 1 for short periods if households are deficit spending (borrowing to consume), but standard Keynesian theory assumes 0 <= MPC <= 1.
What is autonomous consumer spending?
Autonomous spending is the portion of consumption that occurs regardless of income - funded by past savings, credit, or government transfers. It appears as the intercept (a) in the consumption function C = a + MPC x Yd. Even if disposable income fell to zero, households still need to buy essentials, so autonomous spending is typically positive.
How does MPC affect fiscal policy?
A higher MPC amplifies the impact of fiscal stimulus because each round of spending becomes income that is then largely re-spent. Governments trying to boost GDP prefer high-MPC populations (often lower-income households who spend a greater share of new income). Economists use the multiplier to estimate how much GDP will rise for a given increase in government spending or tax cut.
What is a typical MPC value?
Empirical estimates for developed economies generally place the aggregate MPC between 0.5 and 0.9, with the US often cited around 0.6-0.8. Lower-income households tend to have higher MPCs (spending a larger share of additional income) while higher-income households tend to save more of additional income, leading to lower MPCs.