VA Math: Why 50% + 30% Doesn't Equal 80%

If you have more than one service-connected disability, you have probably run into the most confusing part of the entire VA compensation system: the combined rating. A veteran with a 50% rating and a 30% rating does not have an 80% combined rating. They have 70%. A veteran rated at 80% who wins a brand-new 20% rating may see their combined rating change by exactly nothing.

This isn’t an error, and it isn’t the VA shortchanging you. It’s a deliberate formula written into federal regulation - 38 CFR 4.25, known informally as “VA math.” Once you understand the logic behind it, you can predict your combined rating accurately and make smarter decisions about which claims are actually worth pursuing.

Why the VA Doesn’t Simply Add Ratings

The VA rating system is built on the concept of a “whole person.” You start at 100% efficient - a full, unimpaired capacity to work and function. Each disability rating represents a percentage reduction of whatever capacity you have left, not a percentage of the original whole.

Here’s the key idea from the regulation: a person with a 60% disability is considered 40% efficient. If that person then develops a second disability rated at 30%, the VA doesn’t subtract another 30 points from the original 100. Instead, the second condition takes 30% of the remaining 40% efficiency.

The logic is that you can never be more than 100% disabled. If ratings simply added together, a veteran with ratings of 50%, 30%, and 40% would be “120% disabled,” which is mathematically meaningless under a whole-person model. VA math keeps every possible combination between 0 and 100.

How the Combined Ratings Table Works

The combined ratings table in 38 CFR 4.25 does the arithmetic for you, but the underlying process is straightforward:

1. List your ratings from highest to lowest. The regulation requires combining in order of severity, starting with the largest rating.
2. Apply the first rating to 100. A 50% rating leaves you 50% efficient.
3. Apply the next rating to what remains. A 30% rating takes 30% of the remaining 50, which is 15. Add that to the first rating: 50 plus 15 equals a combined value of 65.
4. Repeat for every additional rating, always applying the next percentage to the efficiency that’s still left.
5. Round the final result to the nearest number divisible by 10.

On the official table, you find the higher rating in the left column and the lower rating along the top row. The number where they intersect is the combined value before rounding.

Worked Examples, Step by Step

Example 1: 50% + 30%. The 50% rating leaves 50% efficiency. The 30% rating takes 30% of that remaining 50, which is 15. Combined value: 50 + 15 = 65. Rounded to the nearest 10, that becomes a 70% combined rating.

Example 2: 40% + 20%. The 40% rating leaves 60% efficiency. The 20% rating takes 20% of 60, which is 12. Combined value: 40 + 12 = 52. That rounds down to 50%.

Example 3: 60% + 40% + 20%. This is the regulation’s own illustration. Start with 60%, leaving 40% efficiency. The 40% rating takes 40% of 40, which is 16, for a running total of 76. Then the 20% rating takes 20% of the remaining 24% efficiency, which is 4.8, bringing the value to roughly 81 on the table. Rounded, the combined rating is 80%.

Notice that you do not round between steps. You carry the intermediate table value forward and round only once, at the very end.

The Rounding Rule: Nearest 10, Fives Go Up

The final combined value is converted to the nearest number divisible by 10, and values ending in 5 are adjusted upward. So a combined value of 64 becomes 60%, while 65 becomes 70%. A value of 84 becomes 80%, and 85 becomes 90%.

This rounding step is where a lot of veterans get frustrated - and where a few get a pleasant surprise. Landing on 65 instead of 64 is the difference between a 60% and a 70% payment. It also means two veterans with different underlying conditions can end up at the same payable rating even though their raw combined values differ by as much as 9 points.

The Bilateral Factor: A Small Bonus for Paired Limbs

There is one place where VA math works in your favor beyond the standard table: the bilateral factor under 38 CFR 4.26. When you have compensable disabilities affecting both arms, both legs, or paired skeletal muscles, the VA recognizes that impairment on both sides of the body is more disabling than the same conditions on one side.

Here’s how it works. The ratings for the paired extremities are combined first, and then 10% of that combined value is added on top. The result is treated as a single rating and slotted into the severity order before combining with everything else.

The regulation’s example uses ratings of 60%, 20%, 10%, and 10%, where the two 10% ratings affect paired extremities - say, both knees. The two 10% ratings combine to 19. Adding the bilateral factor of 1.9 brings the value to 20.9, which is carried as 21. The severity order is now 60, 21, and 20. Combining 60 and 21 yields 68; combining 68 and 20 yields 74; and 74 rounds to a 70% combined rating.

The bilateral factor rarely swings a rating by a full 10 points on its own, but in close cases - especially when your raw value is sitting at 64 or 74 - those extra fractions can push you over a rounding threshold.

Why New Ratings Have Diminishing Returns

Because each new rating only applies to your remaining efficiency, every rating you add is worth less than the one before it. This is the single most important practical takeaway from VA math.

Consider a veteran already rated at 80% combined. An 80% rating leaves only 20% efficiency. A brand-new 20% rating takes 20% of that remaining 20, which is just 4 points, for a combined value of 84 - which rounds right back down to 80%. The veteran won the claim and gained nothing in monthly compensation.

Contrast that with a veteran rated at 30%. The same new 20% rating takes 20% of a remaining 70% efficiency, adding 14 points for a combined value of 44, which rounds to 40% - a full bracket increase in monthly compensation.

This is why climbing from 90% to 100% is so notoriously difficult. At 90%, only 10% efficiency remains. To reach a combined value of 95 - the threshold that rounds up to 100 - you would need enough additional rating to capture half of that last sliver. A single new 50% rating does it (50% of the remaining 10 is 5, and 90 + 5 = 95, which rounds up to 100%), but a stack of new 10% and 20% ratings often won’t move the needle at all.

Planning Your Claims with VA Math in Mind

Understanding the formula changes how you think about your claim strategy. Low ratings matter most when your combined rating is low. Higher-value claims - conditions that could realistically rate at 30%, 50%, or 70%, and increases to existing ratings - matter most when your combined rating is already high. And bilateral conditions are always worth identifying, because the bilateral factor is free math in your favor.

You don’t need to memorize the table. Our free calculator applies the exact 38 CFR 4.25 formula, handles the ordering and rounding automatically, and shows you how a potential new rating would - or wouldn’t - change your bottom line. Run your numbers before you file, and you’ll know exactly what a successful claim is worth.