VA Combined Disability Rating Math: The Bilateral Factor and TDIU Explained
A standard combined-ratings calculation leaves out two rules. The bilateral factor can raise a rating for paired-limb disabilities, and TDIU pays the 100% rate to veterans who cannot work.
Two VA rules sit outside the standard combined-ratings formula. The bilateral factor (38 CFR 4.26) applies when a veteran has compensable disabilities in paired limbs, such as both legs or both arms. The paired ratings are combined, and 10% of that value is added before the result joins the other ratings. TDIU (Total Disability based on Individual Unemployability) pays at the 100% rate when service-connected disabilities prevent substantially gainful work. It generally requires one disability rated 60% or more, or a combined 70% or more with one disability at 40% or more.
Our VA Disability Calculator applies the standard "whole person" formula, in which each rating is applied to the capacity that remains. It does not apply the bilateral factor or TDIU, because both depend on facts about your case. This article explains each one with numbers.
The bilateral factor
The factor applies when you have compensable disabilities affecting both arms, both legs, or paired skeletal muscles. Under 38 CFR 4.26:
- The ratings for the paired limbs are combined in the usual way.
- Ten percent of that combined value is added.
- The result is treated as one rating and combined with the veteran's other ratings.
An example where it changes the outcome. A veteran has a 30% back rating and 10% for each knee.
| Step | Without the bilateral factor | With the bilateral factor |
|---|---|---|
| Knees | 10% and 10%, combined one at a time | 10% and 10% combine to 19%. Add 1.9 to get 20.9, rounded to 21%. |
| Combined value | 43 | 45 |
| Final rating (rounded to nearest 10) | 40% | 50% |
| Monthly pay, veteran alone | $795.84 | $1,132.90 |
Here the factor moves the combined value from 43 to 45, which rounds up to 50% and adds about $337 a month.
It does not always change the result. The regulation's own example uses ratings of 60%, 20%, 10% and 10%, with the two 10% ratings as the bilateral pair. The pair becomes 21%. Then 60 and 21 combine to 68, and 68 and 20 combine to 74, which rounds to 70%. Without the factor the same ratings also come to 74 and round to 70%. The factor matters when it carries the combined value across a rounding point ending in 5.
VA is supposed to apply the bilateral factor automatically. Check your rating decision letter. It lists each disability and should show the bilateral factor where paired limbs are involved. If it is missing, a Veterans Service Organization can help you ask for a correction.
Without Bilateral Factor
Ratings for paired-limb disabilities combine using the standard formula only.
With Bilateral Factor
Paired-limb ratings combine first, then get a 10% addition before joining the rest of the calculation.
TDIU: paid at 100% without a 100% rating
Total Disability based on Individual Unemployability lets VA pay a veteran at the 100% rate when the combined rating is lower, if service-connected disabilities prevent the veteran from holding substantially gainful employment.
The money involved is large. Under current rates, a veteran alone receives $1,808.45 a month at 70% and $3,938.58 at 100%. TDIU closes that gap of about $2,130 a month.
Under 38 CFR 4.16, schedular TDIU generally requires one of these:
- one service-connected disability rated at least 60%, or
- two or more service-connected disabilities with a combined rating of at least 70%, and at least one of them rated 40% or more.
A veteran who does not meet either threshold but cannot work because of service-connected disabilities can be considered for extraschedular TDIU. That is decided case by case and is harder to win.
You can have some income. The regulation separates substantially gainful employment from marginal employment, and marginal employment does not rule out TDIU. Marginal employment generally means earned income at or below the Census Bureau's poverty threshold for one person. The threshold changes each year, and published figures for the current year disagree. If your earnings are near that level, confirm the number with VA or a Veterans Service Organization.
How to apply. File VA Form 21-8940, Veteran's Application for Increased Compensation Based on Unemployability. It asks for your work history and education. Medical evidence that ties your inability to work to your service-connected conditions carries the most weight. An accredited VSO will help you file at no charge.
Frequently Asked Questions
What is the VA bilateral factor?
It is an adjustment under 38 CFR 4.26 for compensable disabilities affecting paired limbs, such as both legs or both arms. The two ratings are combined, and 10% of that combined value is added before the result is combined with the veteran's other ratings.
Does the VA disability calculator on this site include the bilateral factor?
No. It applies the standard combined-ratings formula. The bilateral factor requires knowing which ratings affect paired limbs, so it is not part of a general calculation.
What is TDIU?
Total Disability based on Individual Unemployability. VA pays the veteran at the 100% compensation rate, although the combined rating is below 100%, when service-connected disabilities prevent substantially gainful employment.
What rating do I need to qualify for TDIU?
For schedular TDIU, either one service-connected disability rated at least 60%, or several that combine to at least 70% with at least one rated 40% or more. Veterans below those thresholds who cannot work because of service-connected disabilities may be considered for extraschedular TDIU.
Can I work at all and still receive TDIU?
Yes. Marginal employment does not rule out TDIU. It generally means earned annual income at or below the Census Bureau's poverty threshold for one person.
This article explains general VA bilateral factor and TDIU rules as of October 2026. VA decides whether the bilateral factor applies to particular ratings and whether a work history and income qualify for TDIU. This is general educational information, not legal advice. For help with a claim, contact an accredited Veterans Service Organization (VSO) or a VA-accredited attorney.