How an extra dollar travels through the economy
Economists call the share of an income increase spent on goods and services the marginal propensity to consume. “Marginal” means the next change: it is about what a person does with an additional dollar, not what they spend from their entire income.
If someone spends 80 cents of an extra dollar and saves 20 cents, their marginal propensity to consume is 0.8. The rest is not necessarily idle; it may go toward paying down debt or building savings. The measure simply tracks how much of the new income becomes current spending.
Why the same increase can have different effects
A person who has been postponing groceries, replacing a worn appliance, or catching up on bills may use much of a raise or benefit payment quickly. Someone whose essentials are already covered may be more able to save an added dollar. That is why directing extra income to people with tighter budgets can produce a faster lift in consumer spending—though individual choices vary.
When a purchase becomes another person’s income, some of that money may be spent again. A local shop uses sales revenue to pay workers or suppliers; those recipients may then make purchases of their own. This chain can amplify an initial increase in spending. It is not unlimited: each round leaks away into saving, taxes, debt repayment, or purchases from elsewhere.
The measure therefore helps explain why the source of new income matters, not just its total. An income boost is more likely to show up promptly at checkout when recipients have pressing needs and little room to postpone spending.
