How to write a nexus letter VA can actually use

A patient hands you a page and asks for a letter for their VA claim. It is not a form you have seen before, there is no template in the chart, and the request arrives with no explanation of what the reader is looking for. Most clinicians write something reasonable and never learn whether it helped.

This is what the reader is looking for, and why.

What VA already has, and what it does not

By the time a veteran asks you for this letter, VA usually has the diagnosis and the treatment records. Those establish that a condition exists and that it has been treated. What the file does not contain is a clinician's judgment connecting the present condition to the patient's service.

That connection is called a nexus, and supplying it is the whole purpose of the letter. There is no VA form for it. A signed letter on your letterhead is what the system expects.

The standard is lower than the one you are used to

VA asks whether it is at least as likely as not that the condition is related to service. That phrase has a fixed meaning: a probability of 50 percent or greater.

This is worth sitting with, because it is a lower bar than clinical practice usually asks for. You are not being asked whether service caused the condition beyond reasonable doubt, or to a reasonable degree of medical certainty as that phrase is used in litigation. You are being asked whether the proposition is as likely as its opposite.

If the evidence for and against sits evenly balanced, the standard is met. VA is required to resolve reasonable doubt in the veteran's favor, so an opinion that lands squarely on the fence is a favorable one. Clinicians who are careful by training often write themselves below the threshold without meaning to.

What decides the weight your letter carries

Not your credentials. Not whether you are a VA provider. The reasoning.

An opinion that states a conclusion without explaining it carries little weight no matter who signed it, and an opinion from a community clinician that explains itself carries more than an unexplained one from a specialist. A private provider's opinion is competent evidence, and VA may not discount it merely because it came from outside VA.

So the question to ask yourself is not "am I qualified enough to say this" but "have I said why".

The four things a usable letter contains

Who you are and how you know the patient. Your name, credentials, and specialty, the facility, and the treating relationship with dates. "I have treated this patient for his right foot since December 2025" tells the reader the opinion rests on care, not on a paid review.

What you reviewed. Name the records and their dates. Imaging, operative notes, consults, service treatment records if you have them. If you did not have something, say so — an opinion that is open about its limits is more credible than one that implies a completeness it does not have.

Your reasoning. Two or three sentences that walk from findings to conclusion. This is the part that decides everything.

The opinion, in the standard phrasing. Write it in full:

It is my opinion that it is at least as likely as not (50 percent or greater probability) that [condition] was incurred in or aggravated by [the patient's] military service.

Then sign and date it.

What reasoning actually looks like

Compare two versions of the same opinion.

Without reasoning:

Based on my review of the records and my treatment of this patient, it is at least as likely as not that his right foot condition is related to his military service.

With reasoning:

Hallux valgus is a structural deformity that progresses over years under repeated forefoot loading and pressure from footwear. When I first measured this patient in December 2025 the hallux valgus angle was 24 degrees with degenerative change already visible on weight-bearing films — a deformity of that degree with failure of conservative care reflects a long-standing process rather than a recent one. That course is consistent with his reported onset during active duty, when his training and duties were performed in military boots. It is my opinion that it is at least as likely as not (50 percent or greater probability) that his right foot condition was incurred in or aggravated by his military service.

Same conclusion, same author, same records. The second one is evidence.

Notice what the second version does: it explains the natural history of the condition, anchors the explanation in a specific measurement with a date, and only then connects it to the service history. It does not assert that service caused the deformity. It explains why the timeline fits.

Causation is not the only route

Two other bases are often the accurate ones, and both are frequently missed.

Aggravation. A condition that existed before service, or that exists independently, may have been permanently worsened beyond its natural progression. That is its own basis, and it is the honest answer when a patient clearly had a problem before service that got materially worse during it.

Secondary connection. A condition caused or aggravated by an already service-connected one. An altered gait from a service-connected ankle leading to knee or lumbar problems is the classic pattern. The opinion works the same way: state the link and the reasoning behind it.

If causation is not supportable but aggravation is, say aggravation. Writing the wrong one because it is the one you were asked about helps nobody.

When you cannot answer

Sometimes the honest answer is that the question cannot be resolved on the evidence available. Say so, and say what prevents it — a record you do not have, a study never performed, a period of the patient's history you have no visibility of.

The explanation is the part that matters. An opinion that rests on speculation without explaining why the question is unanswerable is generally treated as carrying no weight at all. One that identifies the specific gap is useful: it tells the veteran what to go and find.

The failures worth avoiding

Conclusion without rationale. The most common, and the most costly.

Hedging past the standard. "It is possible that" and "cannot be ruled out" sit below 50 percent as VA reads them. If you believe the proposition is as likely as not, write that.

Copying the rating criteria. Reciting the language of the rating schedule without a clinical observation behind it reads as coaching and weakens the letter.

Overreach. Do not opine on matters outside your expertise or outside the records. A letter that overstates is easier to discount than one that is narrow and well supported.

Practical points

One page is normal and sufficient. Your letterhead, signed and dated, with your license number and NPI. There is no VA form to complete and no portal to submit through — the letter goes back to your patient, who decides whether to include it in their claim.

VA does not pay for this. Some practices bill the patient for the time as they would for any letter; that is between you and them.

And you may decline. An opinion you do not hold is worth nothing to your patient and less than nothing to their claim.

The short version

Say who you are, what you read, why you think what you think, and then say it in the standard phrasing. The reasoning is the letter. Everything else is the envelope.