How VA Math Works: Combined Ratings & the Bilateral Factor

The one-line answer

The VA does not add your disability ratings. It combines them with an “efficiency” formula so that each new rating only affects the part of you that is still “efficient.” The result is almost always lower than the sum — which is why stacking ratings rarely reaches a schedular 100%.

The efficiency formula (38 CFR § 4.25)

Start at 100% efficiency. For each rating, subtract that percentage of the remaining efficiency, working from highest rating to lowest. Two 50% ratings: 100 → 50% disabled, 50% left → the second 50% takes 50% of the remaining 50% = 25, so 75% combined (not 100%). A 70% + 50% + 30% + 10% lands near 90%.

Only the final combined value is rounded to the nearest 10% (with .5 and above rounding up). Intermediate values are never rounded. That is why 74% still pays at 70% but 75% rounds to 80% — a single point near a bracket edge can change your payment.

The bilateral factor (38 CFR § 4.26)

When you have compensable ratings on both sides of a paired structure — both knees, both shoulders, both arms or legs, or paired skeletal muscles — the VA combines those bilateral ratings, then adds 10% of that combined value before combining with everything else.

Mental health, spine, and internal-organ conditions are not bilateral, even if they affect both sides conceptually. The factor is modest (10% of the bilateral subtotal, not 10 points), but near a rounding edge it can flip a 90% to a 100% — worth checking on your decision letter.

TDIU: the 100% rate without a 100% schedular rating

Total Disability Individual Unemployability (TDIU) pays at the 100% rate when service-connected conditions prevent substantially gainful employment. The usual threshold: one condition at 60%+ OR a combined 70%+ with at least one condition at 40%+. If you are close but not at 100% schedular, TDIU is the path most veterans actually take to the top payment.