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Why VA Math is not adding — 38 CFR §4.25 explained

Updated June 2026 · Source: 38 CFR §4.25

Every veteran hits this wall: you have two 50% ratings, you expect 100%, the letter says 80%. Or you have ratings of 70, 50, 30, 30, 10, 10 — and the VA gives you 90% combined. The math is correct. It's the formula that's counterintuitive — and once you understand it, you can verify any award letter yourself.

The §4.25 "whole-person" formula

VA treats your body as 100% efficient at baseline. Your first (highest) disability reduces that efficiency. The next disability reduces the remaining efficiency — not the original 100%. The chain continues for every disability, then the final number is rounded to the nearest 10%.

The algebraic formula for combining two ratings A and B is:

Combined = A + B × (1 - A)

For three or more ratings, apply the formula sequentially: combine the first two, then combine the result with the third, and so on. Always list highest first.

Worked examples

Example 1 — Two 50% ratings

• Start: 100% efficient.
• First 50% disability → 50% remaining capacity.
• Second 50% reduces that remaining 50% by half → 25% additional reduction.
• Total disability: 50% + 25% = 75%.
• Round to nearest 10% → 80% combined.

Example 2 — 70%, 50%, 30%, 30%, 10%, 10%

• After 70%: efficiency = 30%.
• + 50% of 30% = 15% more → running total 85% → remaining 15%.
• + 30% of 15% = 4.5% → 89.5% → remaining 10.5%.
• + 30% of 10.5% = 3.15% → 92.65% → remaining 7.35%.
• + 10% of 7.35% = 0.735% → 93.39% → remaining 6.62%.
• + 10% of 6.62% = 0.66% → 94.05%.
• Round to nearest 10% → 90% combined.

Example 3 — PTSD 70% + sleep apnea 50% + tinnitus 10%

This is one of the most common three-condition combinations veterans ask about:

• After PTSD 70%: remaining efficiency = 30%.
• + Sleep apnea 50% of 30% = 15% → running total 85% → remaining 15%.
• + Tinnitus 10% of 15% = 1.5% → 86.5%.
• Round → 90% combined.

At 90%, the 2026 monthly rate is $2,362.30 (single, no dependents). At 80% it would be $2,102.15 — a difference of $260.93/month or $3,131.16/year. This is why each tier matters.

Example 4 — Four 30% ratings

Veterans with multiple service-connected musculoskeletal conditions often have several 30% ratings:

• After first 30%: remaining = 70%.
• + 30% of 70% = 21% → 51% → remaining 49%.
• + 30% of 49% = 14.7% → 65.7% → remaining 34.3%.
• + 30% of 34.3% = 10.29% → 75.99%.
• Round → 80% combined.

Four 30% ratings do not make 120%. They make 80% — still a significant result, and potentially TDIU-qualifying depending on single-condition thresholds.

The rounding rule — the part many calculators get wrong

Round to the nearest 10% only at the very end. Never round intermediate steps.

• 65.0% or higher → rounds to 70%
• 64.9% or lower → rounds to 60%
• 55.0% or higher → rounds to 60%
• 54.9% or lower → rounds to 50%

Calculators that round at each intermediate step will produce wrong answers for combinations that cross bracket boundaries mid-calculation. Our calculator carries full decimal precision through every step and rounds only the final output.

The combined ratings table vs. the formula

38 CFR Part 4 includes a printed "Combined Ratings Table" — a grid showing pre-computed results for two-condition combinations. The formula and the table are identical: the table is just the formula computed in advance for whole-number inputs. For more than two conditions, you look up the first two, then look up the result against the third, and so on. Our calculator applies the formula directly so no manual look-up is needed.

VA's rating brackets and why they matter

VA rates disabilities in steps of 10%, and each step triggers a meaningfully different compensation level. The differences between adjacent tiers in 2026:

The 90% to 100% jump is the largest by far because it also opens up TDIU consideration and full P&T (permanent and total) status for eligible veterans.

What to do if your letter looks wrong

If your VA award letter shows a combined rating you believe is incorrect, here is how to verify it:

1. List all rated conditions from the letter, with each condition's individual rating percentage.
2. Run the calculator on this page using only the rated conditions (not conditions under appeal or not yet service-connected).
3. Check whether the bilateral factor applies. Do you have conditions of both arms or both legs? If so, enable the bilateral option — many VA letters omit this bonus.
4. Compare pre-rounding values. If our pre-rounding number is meaningfully different from what VA's math would produce, document the discrepancy.
5. Contact a VSO. Free VSOs at DAV, VFW, American Legion, or your state's veterans department can review the rating decision and file a supplemental claim or appeal if the math is wrong.

Planning your claims strategy with VA Math

Understanding the formula lets you prioritize claims strategically. Because of the diminishing returns in the formula, the highest-impact new condition to add depends on your current combined rating:

• If you are currently at 70%, adding a 30% condition pushes you to 79% → rounds to 80%. That's +$293/month.
• If you are at 80%, adding a 30% condition pushes you to 86% → rounds to 90%. That's +$261/month.
• If you are at 90%, adding a 30% condition pushes you to 93% → rounds to 90%. No change — you need to push past 95% to round to 100%.

This is also why knowing the pre-rounding value matters: a veteran at 92% pre-rounding and 90% rounded needs just one additional condition pushing them past 95% to jump to 100% — a $1,575/month increase.

Bilateral factor and SMC

The combined rating formula is one piece. Two other regulations can significantly change your total:

• Bilateral factor (38 CFR §4.26): If you have conditions of both arms or both legs (or paired skeletal muscles), a 10% bonus on the bilateral sub-total is applied before folding into the rest. See our bilateral factor guide.
• SMC (38 CFR §3.350): Special Monthly Compensation pays additional monthly amounts (SMC-K = $139.87/mo each, SMC-S = $4,408.53/mo, up to R2/T = $11,271.67/mo) for specific conditions. This is on top of or instead of schedular comp. See our SMC guide.

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