What evidence supports a VA disability claim?
A claim can fail even when nobody doubts the condition is real, because nothing in the file connects it to service. Knowing which piece of evidence proves which fact is how you avoid that.
Direct service connection generally needs three things shown by medical or lay evidence: a current disability, an event, injury, or disease in service, and a link between the two, which VA usually expects medical records or opinions to support. A separate paid nexus letter is not required in every claim, and once service connection is granted, evidence of severity sets the rating (38 CFR § 3.303; VA.gov, evidence needed).
Miss one of the three and a direct claim fails, however strong the other two are. Presumptions, covered below, are the main exception. The link is called the nexus, and it is often the hardest of the three to document. Once service connection is granted, a fourth category of evidence decides the percentage: how severe the condition is and how it affects your life.
That is the structure worth organizing your entire claim around. Four buckets, per condition.
Bucket 1: current diagnosis
You must have the condition now. A knee that hurt in 2011 and healed is not a disability. A knee that hurts today, diagnosed today by a clinician, is.
What works: a diagnosis in a treatment record from a VA, military, or private provider. Specific matters: "chronic lumbosacral strain" is a diagnosis, "back pain" alone historically was not, though the VA now recognizes some pain conditions with functional impairment even absent a named pathology. Get a named diagnosis where you can.
What does not work: your belief that you have a condition, a family member's opinion, or a symptom with no clinician attached to it.
Bucket 2: the in-service event
Something in service has to have happened. It can be:
- An injury, the fall, the blast, the vehicle accident, the parachute landing.
- An illness or symptom onset documented in your Service Treatment Records.
- An exposure, burn pits, Agent Orange, contaminated water, hazardous noise, industrial chemicals.
- The nature of the duty itself, flight line noise, repetitive load-bearing, a body-destroying career field.
Your Service Treatment Records are the primary source, which is why the first thing anyone should do is request their complete STRs and keep a personal copy. But records are not the only proof. Personnel records, performance reports, deployment orders, unit histories, hazard registries, and buddy statements all establish what happened.
A missing STR entry is not fatal. It is an obstacle. Lay statements from people who were there, contemporaneous letters or emails home, photographs, and personnel records documenting your duties can all establish an in-service event the medical record missed. Say so explicitly in your claim rather than hoping a rater infers it.
Bucket 3: the nexus, the link
A nexus is the connection between your current condition and that in-service event. It is usually shown by a medical opinion, sometimes by treatment records that already draw the link, and in some cases it is presumed by law. It does not always have to be a separate letter you arrange yourself; see the nexus letter guide for when one helps and what it contains.
How VA weighs the evidence
VA weighs all the evidence for and against the link. When the positive and negative evidence is in approximate balance, the doubt is resolved in the veteran's favor (38 CFR § 3.102; 38 U.S.C. § 5107(b)). That does not mean any evidence at all is enough. A weak or unexplained opinion can be outweighed, so the aim is evidence with reasons behind it.
What a usable nexus opinion contains
An opinion that helps you generally does four things:
- States the diagnosis plainly.
- Uses the standard language, that the condition "is at least as likely as not" related to the in-service event, or caused or aggravated by an already service-connected condition.
- Shows the reasoning. This is what separates a strong opinion from a weak one. A conclusion with no rationale carries little weight. The examiner should explain the mechanism and reference the specific evidence reviewed.
- Confirms what was reviewed, STRs, current records, your reported history.
A one-line note saying "patient's knee pain likely from military service" is far weaker than a paragraph explaining that repetitive load-bearing over a documented twelve-year infantry career, combined with the documented 2014 knee injury, is a recognized mechanism for the current degenerative changes on imaging.
Where a nexus opinion comes from
- Your treating provider. A common starting point. They already know your history, which helps them explain the reasoning, and reasoning is what VA weighs: there is no rule giving a treating provider's opinion extra weight. Some will write one if you ask directly and explain what is needed.
- The VA's own C&P examiner. When VA orders an exam, it often asks the examiner the nexus question. The exam is free, but it is not automatic: VA must provide one only when the conditions described in the next point are met. See the exam guide.
- A private medical opinion. A review by an outside physician that you arrange, and may have to pay for. Worth considering when a C&P examiner returned a negative opinion and you need something to weigh against it. On an initial claim, or a supplemental claim with new and relevant evidence, VA must itself provide an exam or opinion when the record lacks enough medical evidence to decide the claim but shows a current condition or recurring symptoms, an in-service event, and some indication the condition may be linked to that event or to another service-connected condition (38 CFR § 3.159(c)(4)).
When the link is presumed, so no separate opinion is needed
Two important exceptions:
- Presumptive conditions. For certain exposures and service periods, including conditions added by the PACT Act, Agent Orange presumptives, and Camp Lejeune water contamination, the VA presumes the link if you have the condition and the qualifying service. The link still exists in law; it just does not need a separate opinion to prove it. See presumptive conditions, and check the current presumptive-condition categories on VA.gov, because they change.
- Chronic diseases on the regulation's list. For the diseases named in 38 CFR § 3.309(a), such as arthritis, hypertension, and diabetes, a chronic disease shown in service makes later manifestations of the same disease service connected unless they are clearly due to some other intervening cause, and where chronicity in service is open to question, continuity of symptoms since discharge can fill the gap. The same diseases are also presumed service connected if they reach a 10% degree within one year of separation (three years for Hansen's disease and tuberculosis, seven for multiple sclerosis). No condition outside that list counts as chronic for these rules.
Suppose a veteran leaves active duty on October 31, 2024, after twenty years. Service records show no ankle problems, and there is no nexus opinion. In July 2025 an orthopedist X-rays a stiff right ankle, finds degenerative arthritis, and records dorsiflexion to 15 degrees and plantar flexion to 40, both painful.
- On the list? Yes. 38 CFR § 3.309(a) names "Arthritis."
- Enough service? Twenty years clears the 90-day minimum in 38 CFR § 3.307(a)(1).
- Inside the window? The window closes October 31, 2025; July is inside it.
- At 10% or more? Diagnostic Code 5271 starts the ankle at 10% only below 15 degrees of dorsiflexion or 30 of plantar flexion, so these findings fall short. DC 5003 then gives 10% to a major joint, which the ankle is under 38 CFR § 4.45, when X-ray-confirmed arthritis limits its motion noncompensably and painful motion confirms it.
Service incurrence is presumed. The orthopedist's record fills the diagnosis bucket, and the presumption stands in for the in-service event and the nexus. VA can rebut it, but no opinion is needed to raise it.
Had the X-ray come in December 2025, after the window, the presumption would need earlier evidence. 38 CFR § 3.307(c) does not require diagnosis inside the window: an in-window treatment note or a specific, dated lay statement (§ 3.307(b)) showing painful, limited motion can still raise it if diagnosis followed without unreasonable delay. Without either, the claim would ordinarily need a nexus opinion.
Bucket 4: severity and functional impact
Service connection alone can leave a condition at 0%, the rating for a service-connected condition that does not meet the requirements for a compensable (paid) rating (38 CFR § 4.31). Severity evidence is what sets the percentage.
Rating criteria in 38 CFR Part 4 are written in specific, measurable terms: frequency of prostrating attacks, degrees of forward flexion, incapacitating episodes per year, whether a breathing assistance device is required. Your evidence should speak the same language.
Symptom logs
Dated entries, written when the symptom happens, describing what occurred and what you could not do. "March 3, migraine from 0900, dark room until 1600, missed the second half of the workday, took sumatriptan" is worth more than "I get migraines a lot." Frequency is a rating criterion; a log is how you prove frequency.
Lay statements
You are competent to report what you experience and observe, and so are the people around you (38 CFR § 3.159(a)(2)). Your own account belongs in a personal statement; statements from others are covered in lay statements and buddy letters. A spouse describing the nights you do not sleep, a coworker describing the days you leave early, your own account of a flare-up. These are real evidence, not filler. They carry the most weight when they are specific, dated, and consistent with the medical record. VA Form 21-10210 is the standard form; a signed statement works too.
Functional impact
Regulation directs that ratings consider the effect on your ability to function under the ordinary conditions of daily life and work. Say concretely what you cannot do: which tasks at work, which chores, which activities you gave up, what you now need help with. Raters look for this, so put it where they can find it.
Conditions that flare are rated on the whole picture, not on the fifteen minutes you spent in an exam room on a good day. If you are asked how you are doing and answer "fine" out of reflex, that is what goes in the record. Answer with your range: the good days, the bad days, and how often each occurs.
Putting it together
Before you submit, walk each condition through the four buckets and name the specific document that fills each one. If you cannot name a document, that bucket is empty, and an empty bucket is a predictable denial or a lower rating, not a surprise.
| Bucket | Question it answers | Typical evidence |
|---|---|---|
| Diagnosis | Do you have it now? | Treatment record naming the condition |
| Service link | Did something happen in service? | STRs, personnel records, buddy statements |
| Nexus | Are the two connected? | Medical opinion, or a presumption |
| Severity & impact | How bad, how often, what does it cost you? | Symptom logs, treatment notes, lay statements |
Filing with all four covered up front through VA's Fully Developed Claims program is meant to get you a faster decision, because there is less for VA to go and gather (VA.gov).
Evidence and nexus questions
What are the three elements of direct service connection?
A current physical or mental disability, an event, injury, or disease during service, and a link between the two. VA usually expects medical records or opinions to support the link, and may also accept lay evidence. Presumptions are a separate route where the law supplies the link for qualifying service and conditions. How severe the condition is goes to the rating, not to whether it is service connected (38 CFR § 3.303; VA.gov, evidence needed).
What evidence do I need for a VA disability claim?
Evidence for each of the three elements, then evidence of severity: service treatment and personnel records for the in-service event, current treatment records for the diagnosis, a medical opinion or records for the link, and dated symptom logs and statements for how the condition affects daily life and work. VA must make reasonable efforts to get records you identify, such as federal and private treatment records, but you need to tell it where they are and cooperate (38 CFR § 3.159). See getting your records.
Do I always need a nexus letter?
No. The nexus is the link itself, not a particular document. It can come from a VA examiner's opinion, from treatment records, or from a presumption that supplies the link for qualifying service. VA must provide an exam or opinion when the record shows a current condition, an in-service event, and some indication of a link but lacks enough medical evidence to decide the claim. A private opinion can help when the record has no opinion or a negative one (38 CFR § 3.159(c)(4); § 3.307). See nexus letters.
What does "at least as likely as not" mean?
It is the phrase medical opinions commonly use to say a link is as probable as not. On its own it does not decide the claim. VA weighs the whole record, including how well each opinion is reasoned, and when the evidence for and against is in approximate balance, the doubt is resolved in the veteran's favor. It is not a numerical score, and it does not excuse the other elements (38 CFR § 3.102; 38 U.S.C. § 5107(b)).
Sources
- 38 CFR § 3.303, Principles relating to service connection: service connection by evidence or presumption, chronicity and continuity, and diseases first diagnosed after discharge.
- 38 CFR § 3.307(a)-(d), Presumptive service connection: the 90-day service requirement, the one-year window for chronic diseases, the rule that only § 3.309(a) diseases count as chronic, the rule that competent lay evidence can establish the facts, the rule that the diagnosis itself need not fall inside the window if it follows without unreasonable delay, and the rule that VA can rebut the presumption with affirmative evidence (d).
- 38 CFR § 3.309(a), Disease subject to presumptive service connection: the list of chronic diseases presumed service connected, including arthritis, hypertension, and diabetes.
- 38 U.S.C. § 5107(b), Claimant responsibility; benefit of the doubt and Board of Veterans' Appeals, Citation Nr. 22069960 (Dec. 18, 2022): when positive and negative evidence is in approximate balance, the benefit of the doubt goes to the claimant; the Board decision, a non-precedential one applying White v. Principi, 243 F.3d 1378 (Fed. Cir. 2001), states that no additional weight is required for a treating provider's opinion.
- 38 CFR § 3.102, Reasonable doubt: doubt arising from an approximate balance of positive and negative evidence is resolved in the claimant's favor.
- VA.gov, Evidence needed for your disability claim: the three things an original claim must show, the medical or lay evidence that can show them, and the Fully Developed Claims program.
- 38 CFR § 3.159(a)(2) and (c)(4), Department of Veterans Affairs assistance in developing claims: defines competent lay evidence, what a person without medical training can observe and describe, and sets when VA must provide a medical exam or opinion, on a supplemental claim only once new and relevant evidence is presented or secured.
- 38 CFR § 4.71a, Schedule of ratings: musculoskeletal system: Diagnostic Codes 5003 and 5271, degenerative arthritis established by X-ray, rated on limitation of motion, with 10% for a major joint whose limitation is noncompensable but objectively confirmed, the two-joint X-ray-only rule, and the ankle motion thresholds used in the worked example.
- 38 CFR § 4.45, The joints: the shoulder, elbow, wrist, hip, knee, and ankle are major joints for rating arthritis.
- 38 CFR § 4.10, Functional impairment and § 4.31, Zero percent evaluations: ratings rest on the ability to function under the ordinary conditions of daily life, including work, and a zero percent evaluation is assigned when the requirements for a compensable evaluation are not met.
READY214 organizes evidence into exactly these four buckets per condition and shows you which one is empty, so nothing gets submitted half-built. Free, no account needed to look.