The fraction in the change of disposable income that is saved; a change in saving divided by the change in disposable income that caused it.

The ratio of a change in saving to a change in disposable income.

the amount by which savings increase when disposable income increases by a dollar

The proportion of income which is saved per extra dollar earned

Marginal propensity to save is the fraction of an increase in disposable income that is saved. Mathematically, it is defined as the change in savings divided by the change in disposable income.

The marginal propensity to save (MPS) refers to the increase in saving (non-purchase of current goods and services) that results from an increase in income. For example, if a family earns one extra dollar, and the marginal propensity to save is 0.35, then of that dollar, the family will spend 65 cents and save 35 cents. It can also go the other way, referring to the decrease in saving that results from a decrease in income.