AR 601-280, Ch 4:
4–8. Periods of extension of enlistment
a. Individual extensions of enlistment are given in monthly increments, from 1 to a maximum of 23 months, for the minimum amount of time necessary to fulfill the authorized service requirement, (see para 4-9b and 4-9m for exceptions).
b. Extensions for the Bonus Extension and Retraining (BEAR)Program and for soldiers in the ranks of PFC, SPC, or CPL who are on orders for long tour areas, may exceed 23 months, provided they do not exceed the retention control point for their rank at new ETS.
c. Although authorized, subsequent extensions are discouraged. In no case will the combined total of all extensions of the same enlistment exceed 48 months. If an authorized extension, when combined with any prior extensions of the
current enlistment contract, would exceed the 48-month limitation, commanders may request an exception to policy to permit reenlistment. Requests will be submitted to CG, HRC-Alexandria.