It treats your body as one system with an efficiency. Start at 100% efficient. A 30% rating leaves you 70% efficient. The next 20% takes 20% of the remaining 70: that's 14 more, leaving 56. The next 10% takes 10% of what remains: about 5.6, leaving roughly 50.4. The final combined value rounds to the nearest 10: 50%.
Worked example per the combined ratings table (38 CFR 4.25) - illustration, not regulation text
30% back + 20% knee → 44 → 40% combined
+ 10% tinnitus → ~49.6 → rounds to 50%
Three consequences worth knowing
Near the top, rounding is a cliff: 94.9 rounds to 90; 95 rounds to 100.
Paired-arm/leg disabilities get the bilateral factor - a bump for having both members affected - before final rounding.
If combined math can't reach 100 but your conditions genuinely stop you from working, TDIU is a different door to the 100% rate (standeasynetwork.com/resources/va-benefits/tdiu).
THE ONE-SYMPTOM RULE (38 CFR 4.14): The same symptom cannot be rated twice under two diagnoses. Two labels for one set of symptoms earn one rating - but a genuinely separate and additional disability can be rated on its own. Read this explainer before adding percentages in your head: the VA doesn't add, it multiplies remaining efficiency.
Check your own numbers
Use the 2026 VA Disability Pay Calculator (standeasynetwork.com/resources/va-benefits) for current rate tables and dependents math, shown line by line. Then take questions to a free accredited VSO.
In crisis?
If you're a veteran in crisis, call the Veterans Crisis Line now: dial nine eight eight, then press one. Free, confidential, 24/7. Prefer to text? Message 838255. Or chat live at veteranscrisisline.net. For immediate danger, call 911.