what is the difference between mandatory spending and discretionary spending
Discretionary spending. In public finance, discretionary spending is government spending implemented through an appropriations bill. This spending is an optional part of fiscal policy, in contrast to entitlement programs for which funding is mandatory. In the United States, discretionary spending refers to spending set on a yearly basis by decision of Congress. Such spending is usually authorized by Congress in another act.
Over the past 40 years, mandatory spending for programs such as Medicare and Social Security has grown as a share of the budget and relative to GDP, while other discretionary categories have declined. Medicare, Medicaid and Social Security grew from 4.3% of GDP in 1971 to 10.1% of GDP in 2012.