The bilateral factor (38 CFR 4.26)
When a partial disability affects both arms, both legs, or paired skeletal muscles, VA adds a small bonus called the bilateral factor. It exists because losing function on both sides is worse than the whole-person math alone captures.
How it is calculated
- Combine the ratings for the paired disabilities with each other first, using the same combined ratings table.
- Add 10 percent of that combined value to itself. The 10 percent is added, not combined: a paired combined value of 44 becomes 44 + 4.4 = 48 (rounded to a whole number).
- That result counts as one disability and is combined with your remaining ratings in order of severity.
Worked example
Right knee 30%, left knee 20%, and PTSD 50%. The knees combine to 44 (30 + 20% of 70). Ten percent of 44 is 4.4, so the knees count as 48. Then 50 combined with 48 is 74, which rounds to a 70% combined rating. Without the factor the same three ratings give 72, still 70% after rounding; the factor matters most near a rounding boundary, where a few points decide between two ratings and two pay rates. Try it in the calculator: tick Bilateral on both knees.
The 4.26(d) rule: the factor can never hurt you
Occasionally, grouping a low bilateral rating into the factor produces a slightly lower combined value than combining it separately. Since April 2023, paragraph (d) of 38 CFR 4.26 has told VA to leave a bilateral disability out of the factor when doing so produces the higher combined evaluation. The calculator on this site tests every grouping and uses the one that scores highest, the same rule.
When it applies, and when it does not
- Each side of the pair must carry a compensable rating (10% or more). A 0% rating on one side does not trigger the factor for that pair.
- The pair must be the same paired structure: both arms, both legs, or the same paired skeletal muscles on both sides. An arm and a leg do not pair.
- Amputation and loss-of-use ratings have their own rules in the regulation and are not a plain bilateral-factor case.
This page summarizes 38 CFR 4.26 for the arithmetic. Whether a specific condition counts as bilateral is a rating decision in your file, not something a calculator can settle.