If you have a 50% rating and a 30% rating, you'd expect 80%. The VA says 70%. That's not a mistake — it's "VA math," and once you see how it works, it stops feeling like a trick.
The VA never adds your ratings
The rule comes from 38 CFR §4.25, the Combined Ratings Table. Instead of adding percentages, the VA measures how much healthy, working ability you have left, and applies each new disability only to what remains.
Think of yourself as starting at 100% efficient. Your most severe disability takes its bite first. The next disability can only take a bite out of what's still left, not the whole.
A worked example: 50% and 30%
- Start with your highest rating: 50%. You are now considered 50% disabled, with 50% ability remaining.
- Apply the 30% rating to that remaining 50%: 30% × 50 = 15 points.
- Add it on: 50 + 15 = 65.
- Round to the nearest 10%: 70%.
So 50% and 30% combine to a 65 value, which the VA pays at 70%. Not 80%.
Adding a third rating
You keep going the same way, always working from highest to lowest. Say you also have a 20% rating. Take the running combined value (65 from above) and apply 20% to its remaining efficiency:
- Remaining after 65 is 35. Apply 20%: 20% × 35 = 7 points.
- 65 + 7 = 72.
- Round to the nearest 10% → 70%.
So 50% + 30% + 20% still comes out to 70%. Three disabilities, and the overall rating didn't even move to 80%. This is the single most common surprise veterans run into.
The rounding rule matters more than you think
After combining everything, the VA rounds the result to the nearest 10%:
- A combined value of 64 rounds down to 60%.
- A combined value of 65 rounds up to 70%.
That single point can be worth hundreds of dollars a month. It's also why a new secondary condition — even a small one — can push you over a rounding line and raise your whole rating. If you're sitting at a 64 value, the right 10% secondary claim can move you to 70%.
Why two ratings can never reach 100%
Because each rating only chips away at what's left, you get diminishing returns. Two 50% ratings combine to 75 (50, then 50% of the remaining 50 = 25 more), which rounds to 80% — not 100%. To actually reach a 100% combined rating you generally need several high ratings stacked together, which is exactly why the jump from 90% to 100% is so hard.
The shortcut the VA uses
Internally the math is the same as multiplying the "remaining efficiency" each time. Starting at 100% efficiency, a 50% and 30% disability leave you 0.50 × 0.70 = 0.35 (35%) efficient, i.e. 65% disabled — the same 65 we got above. The Combined Ratings Table in §4.25 just pre-computes this so adjudicators don't have to.
What this means for you
Two takeaways. First, never assume your ratings add up — always combine them the VA way before you count on a number. Second, because of rounding, small secondary conditions can matter a lot near a 5-point threshold. Knowing your exact combined value (not just the rounded rating) tells you how close you are to the next level.