The VA does not simply add disability ratings together. Instead, it uses a combined ratings formula often called "VA math" that accounts for the fact that each additional disability reduces a smaller remaining portion of the veteran's overall health. The formula works by starting with the highest-rated disability and applying each subsequent disability to the remaining percentage of non-disabled health.
For example, a veteran with a 50% rating and a 30% rating does not receive 80%. The VA starts with 50%, which leaves 50% of the veteran still considered "healthy." The 30% is then applied to that remaining 50%, which is 15%. So the combined value is 50% + 15% = 65%, which rounds to 70% under the VA's rounding rules.
The VA rounds the final combined value to the nearest 10%. Values ending in 1-4 round down, and values ending in 5-9 round up. So 65% rounds up to 70%, but 64% would round down to 60%. This rounding can make a significant difference in monthly compensation.
The combined ratings table in 38 CFR 4.25 provides pre-calculated results so veterans do not need to perform the math manually. The table shows the combined value for any two percentages, and when there are more than two ratings, the process is applied sequentially — combine the first two, then combine that result with the third, and so on.
Understanding VA math is important for strategic claim filing. Because each additional rating has diminishing returns on the combined percentage, the order of ratings does not affect the final result, but knowing how close you are to a rounding threshold can help you prioritize which claims to file or appeal.