Ask any group of veterans about "VA math" and someone groans. A 50 percent rating and a 30 percent rating don't make 80. They make 70. That isn't an error on your letter, and it isn't the VA shortchanging arithmetic. It is a published formula in federal regulation, and once you see the idea behind it, every number on your decision letter starts making sense.
This guide walks the whole thing: the rule, worked examples you can check yourself, the bilateral factor almost nobody explains, the rounding step that surprises people, and what each combined rating is actually worth per month.
The idea: ratings apply to what's left
The regulation treats a veteran as starting at 100 percent efficiency, meaning full ability. Each disability rating then measures how much of that ability it takes away. The key move is that the second rating applies to the efficiency that remains, not to the original 100.
Think of it like taking pieces of a pie. The first rating takes its slice of the whole pie. The second rating takes its percentage of whatever pie is still on the plate. That is why ratings never add up the way you expect, and why the formula is called combining rather than adding.
The regulation also fixes the order: ratings are combined from the largest to the smallest. The order doesn't change the final answer by much, but it is the published method, and it is what your rater follows.
Worked example: 50 and 30
The most common question in every veteran forum, solved step by step:
- Start at 100 percent efficiency.
- Apply the largest rating first. A 50 percent rating takes half. Combined value so far: 50. Remaining efficiency: 50.
- Apply the 30 percent rating to what remains. Thirty percent of 50 is 15.
- Add it to the running total: 50 + 15 = 65.
- Round to the nearest 10: 65 becomes a 70 percent combined rating.
So the veteran with 50 and 30 is rated 70 percent, not 80. Nothing was taken from you; the two ratings never described 80 percent of a whole person in the first place.
Adding a third rating: 50, 30, and 20
- From above, 50 and 30 combine to 65. Remaining efficiency: 35.
- Apply the 20 percent rating to that 35. Twenty percent of 35 is 7.
- 65 + 7 = 72, which rounds down to 70 percent.
Notice what just happened. A whole additional service-connected disability moved the raw number 7 points, and after rounding it didn't change the official rating at all. That is not a glitch. It is the arithmetic working exactly as written, and it is the single most common source of frustration with a decision letter.
The rounding rule
The combined value always rounds to the nearest 10, and a 5 rounds up. A raw 65 becomes 70. A raw 64 becomes 60. A raw 44 becomes 40.
This is where two veterans can end up further apart than their conditions suggest. A raw 65 and a raw 64 are one point apart in reality and a full 10 points apart on paper, which is a real difference in monthly pay. Rounding is part of the published rule, applied to everyone the same way, and it cuts both directions.
Why each new rating counts for less
Because every rating works on the remaining efficiency, the same 10 percent rating is worth very different amounts depending on where you already stand:
| Your existing combined value | What a new 10% rating adds | New combined value |
|---|---|---|
| 0 | 10 points | 10 |
| 10 | 9 points | 19 |
| 30 | 7 points | 37 |
| 50 | 5 points | 55 |
| 70 | 3 points | 73 |
| 90 | 1 point | 91 |
This is why combined ratings feel like they crawl once you are in the 70s and 80s, and it leads to a fact that surprises nearly everyone: ten separate 10 percent ratings do not equal 100 percent. Run them through the formula and they combine to a raw value of 65, which rounds to 70 percent. The math approaches 100 without ever arriving.
The bilateral factor (arms and legs)
Here is the part that rarely gets explained properly. When both arms or both legs carry service-connected ratings, 38 CFR 4.26 adds an extra step. Those paired ratings are combined first, then 10 percent of that combined value is added, and only then is the result combined with everything else.
The logic is sound: losing strength in one knee is a problem, and losing strength in both is more than twice the problem, because you have nothing to favor.
Worked bilateral example
Say a veteran has a 30 percent rating for a back condition, plus 10 percent for each knee.
- The knees are a bilateral pair, so they combine first: 10 and 10 combine to 19.
- Add the bilateral factor, 10 percent of 19, which is 1.9. That gives 21 (rounded).
- Now combine 21 with the 30 percent back rating, largest first: 30, plus 21 percent of the remaining 70, which is 14.7. Total: 44.7, recorded as 45.
- 45 rounds up to a 50 percent combined rating.
Without the bilateral factor, those same three ratings combine to a raw 43, which rounds to 40 percent. One correctly applied rule, one 10 percent step in official rating, and a meaningful difference in monthly pay for the same conditions.
Two details worth knowing. The pair must be a genuine pair, both arms or both legs; one arm and one leg is not bilateral. And the factor applies to the paired ratings only, not to your whole file.
You can run all of this, including limb tagging, in the free VA disability calculator on this site. It shows every step of the math rather than just an answer.
What each combined rating pays
The combined rating is the number that sets your monthly compensation. These are the published VA rates effective December 1, 2025, for a veteran with no dependents:
| Combined rating | Monthly payment (veteran alone) |
|---|---|
| 10% | $180.42 |
| 20% | $356.66 |
| 30% | $552.47 |
| 40% | $795.84 |
| 50% | $1,132.90 |
| 60% | $1,435.02 |
| 70% | $1,808.45 |
| 80% | $2,102.15 |
| 90% | $2,362.30 |
| 100% | $3,938.58 |
Two things stand out. First, the jumps are not even: moving from 90 to 100 percent is worth more than the jump from 10 all the way to 60. Second, at 30 percent and above you may also receive additional amounts for a spouse, children, or dependent parents, which the table above does not include. Rates change every December 1 with the cost-of-living adjustment.
What the combined rating doesn't capture
The combined rating is not the whole compensation picture. Two other pieces exist and are worth knowing by name, because your decision letter may mention them:
- Special Monthly Compensation (SMC). Additional payments for specific circumstances, such as loss of use of a limb, being housebound, or needing regular aid and attendance. SMC sits outside the combined-rating percentages entirely.
- Total Disability based on Individual Unemployability (TDIU). A way of being paid at the 100 percent rate without a 100 percent schedular rating, when service-connected conditions prevent substantially gainful work.
Whether either applies to you is a claims question, which means it belongs with an accredited representative, and a VSO representative's help is free. This guide covers the math only.
Common surprises on a decision letter
- A 0 percent rating changed nothing. Correct. A noncompensable 0 percent rating adds nothing to the combined value and pays nothing, but it is still an official record that the condition is service connected.
- A new grant didn't move your rating. Also normal, per the diminishing-returns table above, especially once you are past 70.
- Your math and the VA's differ by a point or two. The regulation uses a printed lookup table with whole numbers at each step, so small differences from hand arithmetic are expected. If the gap is 10 points or more, that is worth asking about.
- The effective dates differ by condition. Each grant carries its own effective date, so your combined rating can change partway through a period. More on that in how to read your VA decision letter.
Where this comes from
The combined ratings table is published at 38 CFR 4.25 and the bilateral factor at 38 CFR 4.26, both linked in the sources below. None of it is secret and none of it is discretionary. Your decision letter's combined rating is that table applied to your individual ratings.
Your official combined rating is the one on your VA decision letter, period. This guide exists so the letter makes sense when you read it, not to predict anything. If you use MusterVault, its benefits summary runs this same published formula on the ratings you type in from your own letters. It never estimates a rating from your symptoms, because nothing honest can.