What Is the VA Bilateral Factor? (38 C.F.R. § 4.26 Explained)

The VA bilateral factor, codified at 38 C.F.R. § 4.26, is a mandatory calculation rule requiring the Department of Veterans Affairs (VA) to add an extra 10% to the combined value of disabilities affecting both arms, both legs, or paired skeletal muscles, before that value is combined with any other rated conditions. It is not optional, and it is not the same as simply adding two percentages together.

Most veterans have never heard of it, and that’s exactly the problem. You can serve two decades, get rated for both knees, both shoulders, or nerve damage running down both legs, and never once see the phrase “bilateral factor” explained to you in plain terms. The rule sits inside VA’s combined ratings math (38 C.F.R. § 4.25), and it runs quietly in the background of every rating decision that involves paired limbs. When a rater applies it correctly, you get a small but real bump. When a rater skips it, which happens more than it should, you get shortchanged and nobody flags it for you.

The regulation’s text is maintained by the Electronic Code of Federal Regulations (eCFR), published by the Office of the Federal Register, and mirrored by Cornell Law School’s Legal Information Institute. Both confirm the same operative language: ratings for the right and left sides are combined as usual, and then 10% of that combined value is added, not combined again, before the result moves forward in VA’s math.

Who Qualifies: Both Arms, Both Legs, or Paired Skeletal Muscles

The bilateral factor applies only to three categories of paired disability: both arms (shoulder to fingertip), both legs (hip to toe), or paired skeletal muscles. It does not apply to mismatched pairings, such as one arm and one leg, unless the specific condition involves paired skeletal muscle groups as defined under 38 C.F.R. § 4.26.

If you’re rated for one knee and one shoulder, this rule doesn’t touch you. If you’re rated for both knees, both shoulders, both wrists, both hips, or radiculopathy running into both legs from a back condition, it does. That last one trips people up constantly, because the underlying back condition is a single disability, but the radiculopathy it causes often gets rated separately on each side, and those two separate ratings are exactly what § 4.26 was built for.

The VA Bilateral Factor Math, Step by Step

The bilateral factor calculation happens in three steps: combine the paired-limb ratings using the § 4.25 Combined Ratings Table, add (not combine) 10% of that result to itself, then treat the outcome as a single disability value that gets combined with everything else. This procedure is confirmed in Board of Veterans’ Appeals decision A20004328.

1. Combine the paired sides. Right and left ratings are run through VA’s Combined Ratings Table under § 4.25, which is not simple addition. VA uses a diminishing-returns formula: it takes the higher rating, then applies the lower rating to only the “remaining” percentage of whole-person function.
2. Add 10% of that result. This is the part people miss. VA does not run the combined value back through the table again. It takes flat 10% of the combined number and adds it on top.
3. Treat it as one disability going forward. The new paired total is then combined with your other service-connected conditions using the same § 4.25 table, exactly as if it were a single rated condition.

This three-step sequence matches the procedural language used by the Board in decision A20004328, which states the ratings are “first combined as usual using VA’s Combined Ratings Table” before “10 percent of the resulting value is added (not combined).”

Real Example: How the Bilateral Factor Can Push You From 90% to 100%

Run the numbers on two 20% ratings on both knees, and the combined value under § 4.25 comes out to 36%. Apply the bilateral factor, and it adds roughly 4 more points, producing a paired rating of 40% instead of 36%. That 4-point gap, carried forward into further combination with other conditions, is where the threshold math gets interesting.

The 30%/20% pairing follows the same two-step logic: combine to 44 under the table, then add 10% of 44 (4.4, rounded to 4) for a final paired value of 48%. The exact same math applies to arms as it does to legs. Both shoulders rated 20%/20% land at the identical 40% paired total, just with a slightly different rounding path along the way (3.6 rounds to 4 either way under VA’s standard rounding convention).

Now stretch that 4-point difference across a full rating picture. Say your other service-connected conditions, on their own, already combine to 91% under § 4.25. Add a paired knee rating that was calculated without the bilateral factor (36%): 91 plus 36% of the remaining 9 points equals roughly 94.24, which rounds to 94, and 94 rounds down to a final combined rating of 90%. Now run the same math with the bilateral factor correctly applied (40%): 91 plus 40% of 9 equals 94.6, which rounds to 95, and under VA’s rounding rule, 95 rounds up to a final combined rating of 100%.

How to Check If VA Already Applied the Bilateral Factor to Your Claim

To check whether VA applied the bilateral factor, review the “Evaluation of Your Claim” or codesheet pages of your rating decision letter for the specific phrase “bilateral factor,” or look for your paired-limb ratings grouped together with a percentage that’s higher than what simple combination would produce.

Grab a calculator, or use the § 4.25 combined table directly, and run your own two paired ratings through the three-step process above. If your own number comes out higher than what’s printed on your decision, that gap didn’t come from nowhere. It came from a step VA is required to perform and, in this case, may not have.

When VA Does NOT Apply the Bilateral Factor (The Exception)

VA must apply the bilateral factor whenever § 4.26 conditions are met, with one narrow exception: VA may omit the bilateral factor calculation if applying it would actually lower the combined evaluation rather than raise or maintain it. This exception is confirmed in a 2023 Federal Register rulemaking, “Exceptions to Applying the Bilateral Factor in VA Disability Calculations,” also published through GovInfo.

That exception exists to protect the veteran, not to give VA an excuse to skip the calculation whenever it’s inconvenient. It applies rarely, in edge cases involving how musculoskeletal ratings interact with other combined-evaluation rules. If you’re seeing the bilateral factor left off your codesheet, the far more common explanation is rater oversight, not a legitimate application of this exception.

What to Do If You Think VA Missed It

If your own bilateral factor calculation produces a higher rating than what’s on your decision, request a review of the rating decision, either through a Higher-Level Review, a Supplemental Claim with the § 4.26 math laid out clearly, or by raising it directly with the rater’s office. Bring your worked calculation, your codesheet, and the specific regulation citation.

Accredited veterans service organizations and disability advocates who work these cases regularly describe overlooked bilateral factors as a common, correctable basis for challenging a rating decision. That doesn’t mean every missed calculation gets fixed, or that a fix means a jump to the next threshold. It means the math is checkable, the regulation is on your side, and a documented error is a stronger starting point than a hunch.