A lot of veterans assume VA math works like regular math. If you have a 50% rating and a 30% rating, it seems natural to expect 80%. Then the decision letter arrives, the combined rating says 65% before rounding or 70% after rounding, and suddenly the whole process feels harder to follow than it looked at first.
That confusion is common, and it is not a sign that you missed something obvious. The VA openly explains that a combined disability rating is not the simple sum of individual percentages. Instead, it uses a combined ratings table under federal regulation and rounds the final result to the nearest 10%. The VA’s own example notes that two 10% ratings combine to 19%, not 20% (VA disability ratings overview, 38 C.F.R. § 4.25).
In this post, you’ll learn why combined ratings feel counterintuitive, where veterans often get tripped up, how small changes can affect monthly compensation, and why many veterans take a closer look at the underlying math after a rating decision arrives. If you want a broader foundation first, it may help to start with this plain-English overview of how VA percentages and combined ratings fit together.
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A combined rating is the VA’s way of measuring the overall effect of multiple service-connected disabilities without simply stacking the percentages together. The agency starts with the highest rating, then applies the next rating only to the portion of the body considered “efficient” after the first disability is accounted for. The final number is then rounded to the nearest 10% (VA explanation of combined ratings, 38 C.F.R. § 4.25).
That framework often surprises veterans because the percentages look like additive numbers, but legally they function more like sequential reductions. In practical terms, a 50% condition leaves 50% “unimpaired” for rating purposes. A later 30% condition is then applied to that remaining 50%, not to the original 100%.
That is why two serious conditions can still produce a combined number that looks lower than expected.
Most people read percentages as pieces of the same whole. If a veteran sees 40%, 30%, and 20%, the instinct is to total them up and expect 90%. VA math does not work that way.
Here is the rough logic:
Under the VA’s combined ratings table, 50% and 30% combine to 65%, which rounds to 70%. Two 10% ratings combine to 19%, which rounds to 20% (VA combined ratings table, 38 C.F.R. § 4.25).
This is one reason veterans often feel as if the system is “discounting” later disabilities. In general terms, that feeling comes from how the table is designed. The later ratings are not ignored, but they are being applied to a smaller remaining portion.