Marginal Propensity to Save Calculator
From the change in saving and the change in disposable income, compute the marginal propensity to save: how much of each extra dollar is saved.
Input Data
Results
At a glance:The marginal propensity to save (MPS) is the fraction of an extra dollar of disposable income that is saved. MPS = ΔS ÷ ΔY, where ΔS is the change in saving and ΔY the change in disposable income. MPS plus MPC equals 1.
Formula
MPS = change in saving ÷ change in disposable income.
$$MPS = \dfrac{\Delta S}{\Delta Y}$$$$Multiplier = \dfrac{1}{MPS}$$How to Use
- Enter the change in saving (ΔS).
- Enter the change in disposable income (ΔY).
- Read the MPS.
FAQ
What is MPS and how is it related to MPC?
MPS (marginal propensity to save) measures 'how much of each extra dollar of disposable income people save'. Defined as MPS = change in saving ÷ change in disposable income (ΔS ÷ ΔY), it lies between 0 and 1. MPS and MPC (marginal propensity to consume) are two sides of the same coin: when income rises, the extra money can only go to consumption or saving, so the two shares must sum to 1 — MPC + MPS = 1. Example: if a raise brings HK$800 more disposable income, of which HK$200 is saved and HK$600 spent, then MPS = 200 ÷ 800 = 0.25 and MPC = 600 ÷ 800 = 0.75, adding to exactly 1. This is handy — knowing one gives the other (MPS = 1 − MPC). A high-MPS person tends to save the extra income rather than spend it; MPS reflects the share that 'leaks' out of the consumption cycle. The higher the MPS, the less of an injected spending round is recirculated, and the weaker the boost to demand — directly tied to the spending multiplier (multiplier = 1 ÷ MPS).
How does MPS affect the spending multiplier?
MPS directly determines the size of the spending multiplier, inversely: spending multiplier = 1 ÷ MPS (equivalently 1 ÷ (1 − MPC)). The multiplier is how many times a unit of autonomous spending (e.g. government investment, export rise) ultimately drives up total output, via the 'consumption chain': the first recipient spends part (MPC) and saves part (MPS); the spent part becomes someone else's income, who again spends and saves, and so on. Each round's 'leakage' out of the cycle is exactly the saved portion (set by MPS). So a higher MPS means more leaks each round, the chain converges fast, the amplification is small and the multiplier is small; a lower MPS (people spend more) means less leakage, a longer chain and a larger multiplier. Example: MPS = 0.25 (MPC = 0.75) gives a multiplier of 1 ÷ 0.25 = 4, so HK$1 injected drives HK$4 of output; if MPS falls to 0.2 (MPC = 0.8), the multiplier rises to 5. This is why people's saving and spending propensities are so crucial to fiscal-policy effectiveness — a high-saving (high-MPS) society has a relatively weak multiplier.
Why do higher-income households usually have a higher MPS?
Generally, higher-income households have a higher MPS than lower-income ones, tied to how well basic needs are met. Low-income families must spend most income on necessities — food, rent, transport, utilities — so they have little room to save; when they get extra income, they naturally use it to meet or improve those necessary purchases, so the saved share is low — low MPS, high MPC. High-income households already have their basic needs fully met, so extra income barely changes their living standard and is more likely saved or invested (deposits, stocks, property), giving a higher saved share — high MPS, low MPC. This matters for policy: to stimulate immediate consumption and activity, directing resources to lower-MPS (higher-MPC) lower- and middle-income groups is more effective, because they spend a larger share back into the market; money flowing to high-MPS high earners is mostly saved and weakly boosts immediate demand. That said, in the long run saving is not bad — it funds investment and capital accumulation for growth. Balance between saving and consumption is exactly what the 'paradox of thrift' discusses. MPS is also shaped by age (retirement planning), expectations, interest rates and the wealth effect.
What is the 'paradox of thrift', and why can individual saving be good yet collective saving harmful?
The paradox of thrift, a famous Keynesian macroeconomic paradox, shows that 'what is rational for an individual can produce unintended, even harmful, results at the societal level' — a classic fallacy of composition: what holds for a part need not hold for the whole. At the individual level, saving more and cutting unnecessary spending is usually wise and responsible — it builds an emergency fund, cushions unemployment or accidents, and prepares for retirement and home purchase, raising financial security. That is perfectly rational for one person. The problem arises 'if everyone does it at once'. In the macroeconomy, one person's spending is another's income. When the whole society abruptly saves more and cuts consumption, aggregate demand (consumption) falls; falling demand cuts firms' sales and income, so they reduce output, lay off staff and cut wages; with lower incomes, people can save even less — producing the paradoxical result: everyone tries to save more, yet total income and total saving may fall rather than rise. That is the paradox of thrift: individual thrift, at the aggregate level (especially in a downturn with weak demand), can deepen the recession. Its policy implication: in a recession with weak demand, if everyone plays safe and cuts spending, a vicious cycle forms; then fiscal stimulus (more spending, subsidies) has a role — using government spending to fill the gap in private demand and break the loop. But note this paradox holds mainly in the short run with deficient demand and idle capacity. In the long run, saving is not bad — it funds investment and long-term growth. A healthy economy balances present consumption demand with long-term saving and investment, rather than pushing consumption or saving indiscriminately. This is why MPS matters so much in macro analysis. This tool is for educational estimation only.
Why do higher-income households usually have a higher MPS, and what does it mean for policy?
Generally, higher-income households have a higher MPS than lower-income ones, and understanding why helps design effective fiscal policy. The reason is 'how fully basic needs are met'. Low-income families must spend most income on necessities — food, rent, transport, utilities, medical — leaving almost no room to save; extra income naturally goes first to meeting or improving those necessary purchases, so the saved share is low — low MPS, high MPC. High-income households have needs fully met, so extra income barely changes their living standard and is more likely saved, invested or used for property — higher saved share, high MPS, low MPC. This yields two policy insights. First, on who receives fiscal stimulus: to spur immediate consumption (e.g. against a recession), targeting lower-MPS (higher-MPC) lower- and middle-income groups works better — they spend a larger share of subsidies back into the market, producing a stronger multiplier. This is the logic behind targeted relief (low-income subsidies, vouchers). Second, on income distribution and demand: if income is overly concentrated among high-saving wealthy households while lower-income groups lack purchasing power, overall consumption demand may be weak and momentum sluggish — one reason economists watch how inequality affects aggregate demand. Note MPS is also shaped by age, expectations, interest rates and the wealth effect, so reality varies by person. This tool is for educational estimation only.
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References
Content review: Calculatorism Finance Team. Results are for reference only; please refer to the relevant authorities for the official figures.