Shorthand for the way in which a change in spending produces an even larger change in income. For instance, suppose a government loosens fiscal policy, increasing net public spending by pumping an extra $10 billion into education. This has an immediate effect by increasing the income of teachers and of people who sell educational supplies or build or maintain schools. These people will in turn spend some of their extra money, putting more cash into the pockets of others, who spend some of it, and so on. In theory, this process could continue indefinitely, in which case the multiplier would have an infinite value. In practice, most people save some of their extra income rather than spend it. How much they spend will depend on their marginal propensity to consume. The value of the multiplier can be calculated by this formula:

multiplier = 1 / (1 – marginal propensity to consume)

If the marginal propensity to consume is 0. 5 (50 cents of an extra dollar), the multiplier is 2. In practice, it is often hard to measure the multiplier effect, or to predict how it will respond to, say, changes in monetary policy or fiscal policy.