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Length of service

The length of time that an individual is required to serve as a soldier has varied with country and historical period, whether that individual has been drafted or has voluntarily enlisted. Such service, depending on the army's need for staffing or the individual's fitness and eligibility, may involve fulfillment of a contractual obligation. That obligation might extend for the duration of an armed conflict or may be limited to a set number of years in active duty and/or inactive duty.

As of 2023, service in the U.S. Army is for a Military Service Obligation of 2 to 6 years of active duty with a remaining term in the Individual Ready Reserve. Individuals may also enlist for part-time duty in the Army Reserve or National Guard. Depending on need or fitness to serve, soldiers usually may reenlist for another term, possibly receiving monetary or other incentives.

In the U.S. Army, career soldiers who have served for at least 20 years are eligible to draw on a retirement pension. The size of the pension as a percentage of the soldier's salary usually increases with the length of time served on active duty.