靠国防预算是一个国家为了维持武装力量而支出的费用。

军事费用，在古今中外往往是很大的负担，一旦有战争发生，军费开支往往直线上升，所谓“军旅一兴，费靡巨万”。秦始皇大规模用兵，军费消耗极巨，当时已有“口赋”的人头税。明朝末年军费繁浩，有著名的“三饷加派”，顾炎武在《天下郡国利病书·福建三》中记载：“民田一亩值银七八两者，纳饷至十两。”清代乾隆年间有十全武功，这十场战争，有胜有负，都打得艰苦卓绝。乾隆帝所用军费，约在一亿三千万两白银以上，为了应付繁浩的军费开销，当时盐商总计捐输不下一千三百一十万两银之巨。嘉庆元年（1796年），爆发了白莲教起义，规模浩大，前后历经九年，清廷耗用军费二亿两白银。咸丰年间爆发金田起义，为了镇压太平天国所需庞大的军费，使清政府面临空前的财政危机。咸丰三年（1853年）开征厘金，厘金属于一种地方商业税。为了争饷问题，曾国藩在两江总督任上与江西巡抚沈葆桢争夺江西厘金，双方相峙不下。曾国藩的湘军饷项须自筹，他在给诸弟的信中提到：“饷项已空，无从设法，艰难之状，不知所终。”光绪二十五年，户部奏称：“近年大费有三：曰军饷，曰洋务，曰息债。”

A military budget (or military expenditure), also known as a defense budget, is the amount of financial resources dedicated by a nation to raising and maintaining an armed forces or other methods essential for defense purposes.

Military budgets often reflect how strongly an entity perceives the likelihood of threats against it, or the amount of aggression it wishes to employ. It also gives an idea of how much financing should be provided for the upcoming year. The size of a budget also reflects the entity's ability to fund military activities. Factors include the size of that entity's economy, other financial demands on that entity, and the willingness of that entity's government or people to fund such military activity. Generally excluded from military expenditures is spending on internal law enforcement and disabled veteran rehabilitation. The effects of military expenditure on a nation's economy and society, and what determines military expenditure, are notable issues in political science and economics. There are controversial findings and theories regarding these topics. Generally, some suggest military expenditure is a boost to local economies. Still, others maintain military expenditure is a drag on development.