If consumption is a function of income, then saving is also a function of income.

The marginal propensity to save is equal to 1 minus the MPC. If the MPC increases, the MPS will decrease by an offsetting amount.

In addition to the MPC, we occasionally

Suppose that C = 100 + 0.9 Y

What is the Average Propensity to Consume if income is $1000?

C = 100 + 0.9($1000) = $1000

The APC is therefore equal to 1.

What happens to the APC as income increases to $4000 ?

C = 100 + 3600 = 3700

The APC is therefore 3700/2000 = 0.925