In economics that's called the marginal propensity to spend! And on the lower rungs of the economic ladder the marginal propensity to spend versus the marginal propensity to save is nearly 100% toward spending there and nearly 0% for any savings. So any extra income given via Tax rebates and other methods of income redistribution for lower income households will almost 100% be assured to be immediately spent for some discretionary products purchases as long as the costs of Housing/Food and other necessaries is not eating up all of that beforehand.