The purpose of the saving line is to graphically illustrate the basic saving-income relation for the household sector, which is the foundation of the injections-leakages model used in Keynesian economics.

Two basic types of saving are indicated by the saving line. Autonomous saving is the vertical intercept, or Y-intercept, of the saving line. Induced saving is the slope of the saving line. Of no small importance, the slope of the saving line is also the marginal propensity to save (MPS).

Saving Line

A representative saving line is presented in the exhibit to the right. This red line, labeled S in the exhibit is positively sloped, indicating that greater levels of income generate greater saving by the household sector. This positive relation corresponds to the fundamental psychological law of Keynesian economics.

The two primary characteristics of the saving line are slope and intercept:

• Slope: The slope of the saving line presented here is positive, but less than one. In fact, the slope of the saving line is numerically equal to the marginal propensity to save. In this case the slope is equal to 0.25. The positive slope reflects induced saving--more income means more saving. It also reflects the basic Keynesian psychological law. Click the [Slope] button to illustrate.


• Intercept: The saving line intersects the vertical axis at a value of -$1 trillion. This intersection indicates autonomous saving--saving unrelated to income. Autonomous saving is usually negative, indicating dissaving. This occurs because autonomous consumption is positive. Click the [Intercept] button to illustrate.