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Summary: The VA Disability Calculator uses a unique "VA Math" method to compute combined impairment ratings for veterans with multiple serviceconnected conditions.
Instead of simply adding up the percentages of each condition, the VA uses a combined rating table and a concept of "Whole Person Remaining."
Each subsequent rating is a reduction of the whole person remaining. For instance, if a veteran has a 30% rating for one condition and a 40% rating for another, the total rating is not 70% but 60%. This is because the 30% rating is applied to the 70% of the person not already disabled by the first condition.
In short.
 If the VA finds that a Veteran has multiple disabilities, the VA uses the Combined Rating Table below to calculate a combined disability rating.
 Disability ratings are not additive, meaning that if a Veteran has one disability rated 60% and a second disability 20%, the combined rating is not 80%.
 This is because subsequent disability ratings are applied to an already disabled Veteran, so the 20% disability is applied to a Veteran who is already 60% disabled.
 If you have multiple serviceconnected conditions — VA will combine them using VA Math.
Here's how it works:
 VA starts with the premise that every veteran is 100 percent efficient or not disabled.
 So, if a veteran has a disability rating of 20 percent, the VA sees them as 80 percent nondisabled and 20 percent disabled.
 To include another disability rating of 10 percent, the VA will take 10 percent of the 80 percent nondisabled portion and add it to the existing 20 percent rating.
 This brings the veteran’s total disability rating to 28 percent, which will be rounded to 30 percent.
 This process continues with each disability rating the veteran has.
How does the VA calculate a Veteran's percentage of disability? In this episode of theSITREP, Paul Corbett explains "VA Math" with a simple, stepbystep example.

Transcript 
Chris Attig of the popular Veterans Law Blog explains it.
“Chris, if you add up all my VA Ratings for all my disabilities, I’m over 250% disabled. Why am I still getting paid at a 90% level?”
This question – or one like it – pops into my inbox several times weekly. The short answer is this: when you have multiple ratings for multiple medical conditions, the VA doesn’t ADD them together – it COMBINES them. The VA Combined Ratings Formula causes Veterans – and frankly, many VSOs and attorneys a lot of angst. And it did for me, too, until I learned one thing: the Secret behind VA Math. Before I tell you the Secret to Understanding Veterans Affairs Math, let me show you the easy way to do combined ratings. From Chris Attig, The Veterans Law Blog
VA Math It’s Not Your Mother’s Arithmetic
“VA Math” is how the VA computes combined impairment ratings for multiple conditions in a Veteran’s compensation benefits claim – and it requires that you unlearn real math. When a Veteran has multiple medical conditions that are serviceconnected, and the Veterans Affairs rates each at a different percentage, it would seem that they should add up your percentages to get to a total body impairment rating.
The Easy Way to Do Combined Ratings.
The VA publishes a combined rating table to assist in these calculations. The VA Combined Ratings Table is a table that shows your total impairment percentage when you have more than one disabling serviceconnected condition. List your disabilities, highest to lowest, with the percentage of impairment next to it. Start with the highest, and then one by one, use the above linked combined rating table to combine your remaining rating.
The Secret Behind VA Math and the Combined Ratings Table.
“VA Math” is how the VA computes combined impairment ratings for multiple conditions in a Veteran’s compensation claim – and it requires that you unlearn real math. When a Veteran has multiple medical conditions that are serviceconnected, and the VA rates each at a different percentage, it would seem that they should add up your percentages to get to a total body impairment rating. Things are not as they seem. If a Veteran has a 30% rating for condition A and a 40% rating for Condition B, the total rating is NOT 70%. The VA does not add multiple ratings to get a total rating; instead, they use a formula to get a combined rating. The VA computes the combined rating by considering each disability in order of severity, beginning with the highest evaluation. In the above example, the VA Combined Rating for the two conditions is 60%, not 70%. Here’s the secret to understanding the VA Combined Ratings Table. Your ratings are combined based on the concept of “Whole Person Remaining.” The idea is that if you have NO disabilities, you are a 100% whole person. If you have a 30% disability, you are 30% disabled and 70% whole. Each subsequent rating is a REDUCTION of the whole person remaining.
The VA Combined Ratings Table in Practice.
How does the VA get that combined rating? For example, where Condition A is rated at 30%, and Condition B is rated at 40%, the VA math works like this: Most severe rating: 40%. Second most severe rating: 30%. Combined rating: 60%.
Here’s how we got there: the second rating of 30% is multiplied by the % of the whole person remaining after the 40% rating. In this example, 30% (second rating) is multiplied by 60% (percent of the whole person remaining after 40% rating). This means that while condition A limits the person to a 30degree rate, it only limits 30% of the WHOLE person.
So if the person is 0% impaired (with a 100% whole person value remaining), the condition limits them to 30%. However, if the person is already 40% disabled by another condition, Condition A can only limit the “whole person that remains.” It’s a tough concept to grasp, but in a way, it makes some sense. So, in our example, the second rating of 30% adds 18% to the initial rating of 40%, yielding a combined rating of 58%.
The 58% rating is rounded up to 60%. Does this make sense? I don’t think so – this type of formula is a 50+yearold calculation used by insurance companies in, commonly, workers’ compensation claims. Regardless of the archaic and nonsensical formula, here’s the deal. It’s the way it is. And in the great mess of tangled red tape that is the VA Bureaucracy, there are many fights we need to fight and win before going after this one.
Combined Ratings
Example of Combining Three Disabilities
If three disabilities are ratable at 60 percent, 40 percent, and 20 percent, respectively, the combined value for the first two will be found opposite 60 and under 40 and is 76 percent. This 76 will be found in the left column, followed by the 20 rating in the top row. The intersection of these two ratings is 81. Thus, the final rating will be rounded to 80%.
If the VA finds that a Veteran has multiple disabilities, the VA uses the Combined Rating Table below to calculate a combined disability rating. Disability ratings are not additive, meaning that if a Veteran has one disability rated 60% and a second disability 20%, the combined rating is not 80%. This is because subsequent disability ratings are applied to an already disabled Veteran, so the 20% disability is applied to a Veteran who is already 60% disabled. Below are the steps VA takes to combine ratings for more than one disability, as well as examples using the Combined Rating Table to illustrate how combined ratings are calculated.
 The disabilities are first arranged in the exact order of their severity, beginning with the greatest disability and then combined with the use of the Combined Rating Table below.
Combined Rating Table:
Ten is combined with (not added) 10 and = 19
Click Here to view the Combined Rating Table
10 20 30 40 50 60 70 80 90
19................... 27.......... 35.......... 43.......... 51.......... 60.......... 68.......... 76.......... 84.......... 92
20................... 28.......... 36.......... 44.......... 52.......... 60.......... 68.......... 76.......... 84.......... 92
21................... 29.......... 37.......... 45.......... 53.......... 61.......... 68.......... 76.......... 84.......... 92
22................... 30.......... 38.......... 45.......... 53.......... 61.......... 69.......... 77.......... 84.......... 92
23................... 31.......... 38.......... 46.......... 54.......... 62.......... 69.......... 77.......... 85.......... 92
24................... 32.......... 39.......... 47.......... 54.......... 62.......... 70.......... 77.......... 85.......... 92
25................... 33.......... 40.......... 48.......... 55.......... 63.......... 70.......... 78.......... 85.......... 93
26................... 33.......... 41.......... 48.......... 56.......... 63.......... 70.......... 78.......... 85.......... 93
27................... 34.......... 42.......... 49.......... 56.......... 64.......... 71.......... 78.......... 85.......... 93
28................... 35.......... 42.......... 50.......... 57.......... 64.......... 71.......... 78.......... 86.......... 93
29................... 36.......... 43.......... 50.......... 57.......... 65.......... 72.......... 79.......... 86.......... 93
30................... 37.......... 44.......... 51.......... 58.......... 65.......... 72.......... 79.......... 86.......... 93
31................... 38.......... 45.......... 52.......... 59.......... 66.......... 72.......... 79.......... 86.......... 93
32................... 39.......... 46.......... 52.......... 59.......... 66.......... 73.......... 80.......... 86.......... 93
33................... 40.......... 46.......... 53.......... 60.......... 67.......... 73.......... 80.......... 87.......... 93
34................... 41.......... 47.......... 54.......... 60.......... 67.......... 74.......... 80.......... 87.......... 93
35................... 42.......... 48.......... 55.......... 61.......... 68.......... 74.......... 81.......... 87.......... 94
36................... 42.......... 49.......... 55.......... 62.......... 68.......... 74.......... 81.......... 87.......... 94
37................... 43.......... 50.......... 56.......... 62.......... 69.......... 75.......... 81.......... 87.......... 94
38................... 44.......... 50.......... 57.......... 63.......... 69.......... 75.......... 81.......... 88.......... 94
39................... 45.......... 51.......... 57.......... 63.......... 70.......... 76.......... 82.......... 88.......... 94
40................... 46.......... 52.......... 58.......... 64.......... 70.......... 76.......... 82.......... 88.......... 94
41................... 47.......... 53.......... 59.......... 65.......... 71.......... 76.......... 82.......... 88.......... 94
42................... 48.......... 54.......... 59.......... 65.......... 71.......... 77.......... 83.......... 88.......... 94
43................... 49.......... 54.......... 60.......... 66.......... 72.......... 77.......... 83.......... 89.......... 94
44................... 50.......... 55.......... 61.......... 66.......... 72.......... 78.......... 83.......... 89.......... 94
45................... 51.......... 56.......... 62.......... 67.......... 73.......... 78.......... 84.......... 89.......... 95
46................... 51.......... 57.......... 62.......... 68.......... 73.......... 78.......... 84.......... 89.......... 95
47................... 52.......... 58.......... 63.......... 68.......... 74.......... 79.......... 84.......... 89.......... 95
48................... 53.......... 58.......... 64.......... 69.......... 74.......... 79.......... 84.......... 90.......... 95
49................... 54.......... 59.......... 64.......... 69.......... 75.......... 80.......... 85.......... 90.......... 95
50................... 55.......... 60.......... 65.......... 70.......... 75.......... 80.......... 85.......... 90.......... 95
51................... 56.......... 61.......... 66.......... 71.......... 76.......... 80.......... 85.......... 90.......... 95
52................... 57.......... 62.......... 66.......... 71.......... 76.......... 81.......... 86.......... 90.......... 95
53................... 58.......... 62.......... 67.......... 72.......... 77.......... 81.......... 86.......... 91.......... 95
54................... 59.......... 63.......... 68.......... 72.......... 77.......... 82.......... 86.......... 91.......... 95
55................... 60.......... 64.......... 69.......... 73.......... 78.......... 82.......... 87.......... 91.......... 96
56................... 60.......... 65.......... 69.......... 74.......... 78.......... 82.......... 87.......... 91.......... 96
57................... 61.......... 66.......... 70.......... 74.......... 79.......... 83.......... 87.......... 91.......... 96
58................... 62.......... 66.......... 71.......... 75.......... 79.......... 83.......... 87.......... 92.......... 96
59................... 63.......... 67.......... 71.......... 75.......... 80.......... 84.......... 88.......... 92.......... 96
60................... 64.......... 68.......... 72.......... 76.......... 80.......... 84.......... 88.......... 92.......... 96
61................... 65.......... 69.......... 73.......... 77.......... 81.......... 84.......... 88.......... 92.......... 96
62................... 66.......... 70.......... 73.......... 77.......... 81.......... 85.......... 89.......... 92.......... 96
Table I—Combined Ratings Table (cont.)
10 20 30 40 50 60 70 80 90
63................... 67.......... 70.......... 74.......... 78.......... 82.......... 85.......... 89.......... 93.......... 96
64................... 68.......... 71.......... 75.......... 78.......... 82.......... 86.......... 89.......... 93.......... 96
65................... 69.......... 72.......... 76.......... 79.......... 83.......... 86.......... 90.......... 93.......... 97
66................... 69.......... 73.......... 76.......... 80.......... 83.......... 86.......... 90.......... 93.......... 97
67................... 70.......... 74.......... 77.......... 80.......... 84.......... 87.......... 90.......... 93.......... 97
68................... 71.......... 74.......... 78.......... 81.......... 84.......... 87.......... 90.......... 94.......... 97
69................... 72.......... 75.......... 78.......... 81.......... 85.......... 88.......... 91.......... 94.......... 97
70................... 73.......... 76.......... 79.......... 82.......... 85.......... 88.......... 91.......... 94.......... 97
71................... 74.......... 77.......... 80.......... 83.......... 86.......... 88.......... 91.......... 94.......... 97
72................... 75.......... 78.......... 80.......... 83.......... 86.......... 89.......... 92.......... 94.......... 97
73................... 76.......... 78.......... 81.......... 84.......... 87.......... 89.......... 92.......... 95.......... 97
74................... 77.......... 79.......... 82.......... 84.......... 87.......... 90.......... 92.......... 95.......... 97
75................... 78.......... 80.......... 83.......... 85.......... 88.......... 90.......... 93.......... 95.......... 98
76................... 78.......... 81.......... 83.......... 86.......... 88.......... 90.......... 93.......... 95.......... 98
77................... 79.......... 82.......... 84.......... 86.......... 89.......... 91.......... 93.......... 95.......... 98
78................... 80.......... 82.......... 85.......... 87.......... 89.......... 91.......... 93.......... 96.......... 98
79................... 81.......... 83.......... 85.......... 87.......... 90.......... 92.......... 94.......... 96.......... 98
80................... 82.......... 84.......... 86.......... 88.......... 90.......... 92.......... 94.......... 96.......... 98
81................... 83.......... 85.......... 87.......... 89.......... 91.......... 92.......... 94.......... 96.......... 98
82................... 84.......... 86.......... 87.......... 89.......... 91.......... 93.......... 95.......... 96.......... 98
83................... 85.......... 86.......... 88.......... 90.......... 92.......... 93.......... 95.......... 97.......... 98
84................... 86.......... 87.......... 89.......... 90.......... 92.......... 94.......... 95.......... 97.......... 98
85................... 87.......... 88.......... 90.......... 91.......... 93.......... 94.......... 96.......... 97.......... 99
86................... 87.......... 89.......... 90.......... 92.......... 93.......... 94.......... 96.......... 97.......... 99
87................... 88.......... 90.......... 91.......... 92.......... 94.......... 95.......... 96.......... 97.......... 99
88................... 89.......... 90.......... 92.......... 93.......... 94.......... 95.......... 96.......... 98.......... 99
89................... 90.......... 91.......... 92.......... 93.......... 95.......... 96.......... 97.......... 98.......... 99
90................... 91.......... 92.......... 93.......... 94.......... 95.......... 96.......... 97.......... 98.......... 99
91................... 92.......... 93.......... 94.......... 95.......... 96.......... 96.......... 97.......... 98.......... 99
92................... 93.......... 94.......... 94.......... 95.......... 96.......... 97.......... 98.......... 98.......... 99
93................... 94.......... 94.......... 95.......... 96.......... 97.......... 97.......... 98.......... 99.......... 99
94................... 95.......... 95.......... 96.......... 96.......... 97.......... 98.......... 98.......... 99.......... 99
 The degree of one disability will be read in the left column and the degree of the other in the top row, whichever is appropriate.
 The figures appearing in the space where the column and row intersect will represent the combined value of the two.
 This combined value is rounded to the nearest 10%.
 If there are more than two disabilities, the combined value for the first two will be found as previously described for two disabilities.
 The exact combined value (without rounding yet) is combined with the degree of the third disability.
 This process continues for subsequent disabilities, and the final number is rounded to the nearest 10%.
Source: What’s the Secret to Understanding the Veterans Affairs Combined Ratings Table? Chris Attig The Veterans Law Blog