The bilateral factor is a provision under 38 CFR 4.26 that provides additional compensation when a veteran has disabilities affecting both paired extremities — both arms, both legs, or paired skeletal muscles. The rationale is that bilateral impairment causes greater functional limitation than the same impairment on only one side.
The bilateral factor adds 10% to the combined value of the paired disabilities before combining them with any other ratings. For example, if a veteran has a 20% rating for the left knee and a 10% rating for the right knee, the combined value of those two ratings using VA math is 28%. The bilateral factor adds 10% of that 28% (which is 2.8%, rounded to 3%), making the bilateral combined value 31%. This 31% is then combined with any other disabilities using VA math.
The bilateral factor applies to conditions of the arms, legs, or paired skeletal muscles. It does not apply to conditions that are not considered paired extremities — for example, a back condition and a knee condition would not qualify. However, both knees, both shoulders, both ankles, or any combination of bilateral limb conditions would qualify.
This factor is often overlooked by veterans who file claims one at a time rather than considering the strategic benefit of establishing bilateral conditions. If you have a service-connected right knee condition and also have problems with your left knee, filing for the left knee can trigger the bilateral factor and increase your combined rating beyond what VA math alone would produce.