Every veteran who has multiple service-connected conditions eventually runs into the same frustrating realization: VA disability ratings do not add up the way you think they should. If you have a 70% rating for one condition and a 30% rating for another, simple math says you should be at 100%. But the VA does not use simple math. Using the VA's combined rating formula, 70% + 30% equals 79%, which rounds to 80%. If you just want your combined number without doing the math by hand, run your ratings through the free VA Disability Calculator linked in the tools below. This article explains why the number comes out the way it does, and more importantly, how to break the 90 percent trap that this formula creates for so many veterans. This is not a mistake. It is not the VA trying to cheat you. It is a specific mathematical formula that the VA has used for decades, and understanding it is essential if you want to maximize your rating and your monthly compensation.
The VA combined rating formula is based on a concept called 'whole person theory.' The idea is that you start at 100% healthy, and each disability takes away a percentage of your remaining health. Here is how it works step by step. Start with 100% (representing a fully healthy body). Your highest-rated condition is applied first. If it is 70%, it takes away 70% of your whole body efficiency, leaving you at 30% remaining. Your next condition is applied to the remaining percentage, not the original 100%. A 30% rating applied to your remaining 30% takes away 9% (30% of 30%), leaving you at 21% remaining. Your combined disability is 100% minus 21% remaining, which equals 79%. The VA rounds to the nearest 10%, so 79% rounds to 80%. This is why two conditions rated at 50% each do not equal 100%. The first 50% leaves 50% remaining. The second 50% takes half of the remaining 50%, which is 25%. Total disability: 75%, which rounds to 80%.
Let us walk through several common scenarios to see how VA math plays out in practice. Scenario 1: A veteran has PTSD at 50%, a knee condition at 20%, and tinnitus at 10%. Start at 100%. Apply 50%: remaining 50%. Apply 20% to remaining: 50% minus 10% (20% of 50%) equals 40% remaining. Apply 10% to remaining: 40% minus 4% (10% of 40%) equals 36% remaining. Combined: 100% minus 36% equals 64%, which rounds to 60%. Scenario 2: A veteran has back pain at 40%, migraines at 30%, and sleep apnea at 50%. Start at 100%. Apply 50% first (highest): remaining 50%. Apply 40%: remaining 30%. Apply 30%: remaining 21%. Combined: 79%, rounds to 80%. Notice how the order matters for the calculation but not the result. The VA always applies the highest rating first, but the final combined number is the same regardless of order.
There is one exception to the standard combined rating formula that can work in your favor. The bilateral factor applies when you have conditions affecting both sides of a paired body part, such as both knees, both shoulders, or both ankles. When the bilateral factor applies, the VA first combines the bilateral conditions together, then adds 10% of the combined bilateral rating as a bonus before combining it with your other conditions. For example, if you have a 20% rating for your left knee and a 10% rating for your right knee, the VA combines them to 28%, then adds 10% of 28% (2.8%), giving you 30.8% for the bilateral conditions before combining with your other ratings. This small bonus can sometimes be the difference between rounding up to the next 10% bracket, which means more money every month.
The 90% trap is one of the most common and frustrating situations in the VA claims system. Getting from 90% to 100% using the combined rating formula is extremely difficult. At 90%, you only have 10% remaining healthy body efficiency. To reach 95% (which rounds to 100%), a new condition would need to take away 50% of your remaining 10%, which means you need an additional condition rated at 50% or higher. Many veterans with multiple conditions rated between 10% and 30% find that adding another condition barely moves their combined rating. Going from 90% to 91% or 92% still rounds to 90%. This is why Total Disability Individual Unemployability (TDIU) exists. If your service-connected conditions prevent you from maintaining substantially gainful employment, you can be paid at the 100% rate even if your combined rating is lower. The difference between 90% and 100% is $1,576.28 per month in 2026, so TDIU is worth exploring if you are stuck at 90%.
Understanding VA math gives you a strategic advantage when planning your claims. File for all conditions at once. Each condition you add increases your combined rating, even if the individual ratings seem small. A 10% rating for tinnitus applied to a remaining 20% only adds 2%, but combined with other small ratings, these add up. Focus on secondary conditions. If you have a 70% rating for your back, conditions like radiculopathy, depression, and sleep problems that are secondary to your back condition can each add percentage points to your combined rating. Use our Combined Rating Calculator to model different scenarios before you file. Knowing how VA math works lets you prioritize which conditions to file for first and understand exactly how each additional rating will affect your monthly compensation. Remember: even a condition rated at 0% (service-connected, non-compensable) has value. It establishes service connection, which can be increased later if the condition worsens, and it can support secondary claims for related conditions.