Relatie tussen inkomen, consumptie en sparen

Disposable income refers to the income that remains after taxes—income that households use either for consumption or saving.

Consider Emily, a recent college graduate earning a disposable income of $4,000 per month. She spends $3,200 and saves $800. A year later, her monthly income rises to $5,500. Her spending increases by $800, reaching $4,000, while her savings grow by $700 to $1,500. With more income in hand, Emily decided to spend a bit more—and save the rest.

At lower income levels, a larger portion of income tends to go toward essentials, leaving less room for saving. As income increases, both consumption and saving tend to rise, though not always at the same rate.

To understand how consumption affects national output, economists examine how households divide each additional dollar of income. Part of it is spent, stimulating demand; the rest is saved, contributing to future investment.

These choices are not arbitrary—they follow observable patterns. These patterns are captured by the consumption function and the saving function.