A nexus letter is a written opinion from a doctor about whether a condition you have today is connected to your military service. The VA calls that connection the "nexus," and in a lot of claims it is the piece that decides how things turn out.
I'm a family physician and a Navy veteran, and most of my working day is spent reading service records and medical charts to figure out what they really show. What follows is what I'd tell you if you sat down across from me and asked, "What is this letter, and do I actually need one?"
The three things every claim needs
To connect a condition to service, the VA looks for three things:
- A current diagnosis. A doctor has put a name to what you're dealing with now.
- Something that happened in service. An injury, an illness, an exposure, or an event, written down somewhere or described by you and people who were there.
- A link between the two.
The first two usually live somewhere in your records. The third often doesn't. Your file can show a knee injury in 2009 and arthritis in that knee today and still say nothing about whether one led to the other. Connecting them is a medical question, so it takes a medical opinion. That opinion is the nexus letter, and knowing what a nexus letter costs up front is part of deciding whether pursuing one makes sense for your claim.
What "at least as likely as not" means
You'll see this phrase in almost every nexus letter, and it matters more than any other sentence on the page.
It means the odds are even or better. When a doctor writes that your condition is "at least as likely as not" related to service, they are not saying they're certain. They're saying that after reading your records and the medical research, the connection to service is at least as likely as any other explanation. That's the bar the VA uses, and when the evidence is evenly balanced, the tie goes to the veteran.
Words like "could be related," "may be connected," or "it's possible" don't reach that bar. The VA reads them as a guess, and a guess carries very little weight.
Two roads to the same place: direct and secondary
A direct claim says the condition started in service or grew out of something that happened there. Hearing damage from years on a flight line is the classic example.
A secondary claim says the condition was caused, or made worse, by something the VA already rates. Say the VA already rates your knee. Years of favoring that knee can change the way you walk, and a changed gait can wear on the hip or the lower back. A secondary claim for the hip asks the VA to connect it to the knee instead of to anything that happened in uniform.
Secondary claims are where a good letter earns its keep, because the reasoning is the whole case. Nobody wrote "your hip will hurt in ten years" in your service record.
What a strong letter actually contains
A reviewer can usually tell within a minute whether a letter was written about you or about someone like you. The strong ones have a few things in common.
- It shows the doctor read your records. It names the documents, the dates, and the findings. An opinion built on a phone call and a questionnaire won't hold up against a VA examiner who went through your whole file.
- It uses the VA's standard. "At least as likely as not," stated plainly.
- It explains the how. Not "this condition is common in veterans," but how your particular service, injury, or rated condition led to what you have now, step by step.
- It deals honestly with other explanations. Age, weight, a civilian job, smoking, family history. If there's an obvious alternative, a good letter addresses it and explains why the service connection is still at least as likely. If the letter ignores it, the VA examiner won't.
- It cites research that fits. Two or three studies that speak to your situation are worth more than a long list that only loosely relates.
- It's signed by a licensed physician who states their credentials, so the reader knows whose judgment they're weighing.
What a strong letter looks like for specific conditions
Everything above applies to every claim. Some kinds of conditions add checkpoints of their own.
Mental health conditions
- It confirms the diagnosis. The letter confirms the current psychiatric diagnosis instead of just repeating a label from the chart, and it sorts out overlaps the records leave unclear, such as depression versus an adjustment disorder, or whether PTSD and depression are two separate conditions.
- It lays out the timeline. What happened in service, when the symptoms began, and the diagnoses and treatment since then.
- It names the primary condition in a secondary claim. If the claim is that a condition the VA already rates, such as chronic pain, a TBI, or sleep apnea, led to depression or anxiety, the letter names that rated condition and explains how it led to the mental health condition, stating the direction plainly.
Joint conditions
- It describes your actual duties. The physical demands of an infantry job and an administrative job are very different, and the letter should say what yours were, drawing on your service treatment records and job specialty (MOS) records.
- It ties the imaging to your history. Where there are imaging or operative reports, a strong letter explains whether the pattern of damage they show, where the joint is worn and how, fits the kind of loading your service involved.
- It explains the pathway in a secondary claim. When a joint problem is claimed as caused by a rated condition, for example knee pain that followed a rated back condition, the letter explains how the back condition changed the way you walk and whether the knee symptoms followed the back condition in time.
- "Military service is physically demanding" is not reasoning. The mechanism has to be specific to you.
Skin conditions
- It reads the skin-specific records. Dermatology notes, biopsies, and patch testing, along with your duty stations and deployment records.
- It describes the course. When the skin symptoms first appeared, during or after service, what treatment has been needed, and whether the condition comes and goes in flares or stays continuous.
- It matches the reasoning to the kind of claim. For a chemical or other job exposure, it describes the documented exposure and how that exposure causes the diagnosed condition. For a sun-related condition such as skin cancer, it places the sun exposure in your duty assignments and explains how cumulative sun damage produces the condition. For a skin condition claimed as secondary, such as psoriasis claimed as caused by service-connected PTSD, it explains the pathway from the rated condition to the skin disease, with research that fits.
What the Board of Veterans' Appeals decided
We read Board of Veterans' Appeals decisions from 2021 to 2025 and counted every service-connection appeal the Board decided for the most common conditions. For these five, appeals with a private medical opinion in the record were granted about twice as often as appeals without one:
- Sleep apnea: 86% granted with a private opinion (2,794 of 3,263), 45% without (2,379 of 5,337)
- Knee: 74% with (1,242 of 1,683), 36% without (2,310 of 6,403)
- Hip: 69% with (407 of 586), 30% without (679 of 2,253)
- Ankle: 68% with (319 of 469), 30% without (723 of 2,387)
- Hearing loss: 68% with (1,292 of 1,893), 35% without (3,327 of 9,604)
The Board often says so in its own words. In at least 670 sleep apnea grants, it wrote that it found the private opinion persuasive or probative. One decision put it simply: "The Board finds the private sleep apnea opinion to be the most probative evidence of record."
The Board is just as clear about what doesn't work. Across these five conditions, most denials (86% to 92%) had no private opinion in the file at all. When the Board did set an opinion aside, the reasons repeat:
- No sign the doctor read the records: "There is no indication that the private physician reviewed the service records or other treatment records."
- Hedged wording: an opinion "too vague and speculative to be probative."
- A wrong fact: an "inaccurate factual assumption that renders the private opinion of no probative value."
- A conclusion with no reasoning behind it.
Some claims fail before anyone gets to cause. About half of the PTSD denials we reviewed came down to no qualifying PTSD diagnosis. About half of hearing loss denials found the hearing test didn't meet VA's threshold for a disability. A nexus letter can't fix a missing diagnosis, and a good physician will tell you that up front.
Not every condition works this way. Tinnitus was usually granted with or without a private opinion, because the veteran's own account of when the ringing started often carries the claim.
Veterans who get private opinions may also have stronger cases to begin with, so read these numbers as what happened alongside a private opinion, not as a promise. These are Board of Veterans' Appeals decisions from 2021 to 2025, the appeal level. They do not reflect how your regional office decides claims, and no single number predicts an individual case. How we got these numbers.
When you might not need one
I would rather tell you this up front than sell you something you don't need.
- Presumptive conditions. For some conditions and some kinds of service (certain Agent Orange, Gulf War, and burn pit exposures under the PACT Act, for example), the law presumes the connection. If your condition and your service both fit, the VA shouldn't be asking for a nexus opinion.
- It's already in your records. If your service records show the condition while you were in, and it has been documented ever since, the VA may be able to connect it without outside help.
- The VA examiner already agreed. If your exam came back favorable, a second opinion may add little.
If the VA can already see the connection, save your money.
When a letter tends to matter most
- The condition showed up years after you got out.
- It's a secondary claim, tied to something the VA already rates.
- A VA examiner gave a negative opinion and you need a medical answer to it.
- Your service records are incomplete, or don't mention what happened.
- Your denial letter says there's no link to service.
What a nexus letter is not
It isn't a rating. The VA decides whether a condition is service connected and how much it's rated. The letter doesn't set a percentage.
It isn't a guarantee. It's evidence, and good evidence, but the VA makes the decision.
It isn't legal advice. A physician can explain the medicine. For questions about forms, deadlines, or which kind of review to ask for, a VSO or an accredited representative is the right person.
Why your own doctor might say no
Plenty of veterans ask their regular doctor first, and plenty of those doctors say no. Usually it isn't personal. Writing a good nexus letter means reading years of records, looking up the research, and writing to a standard most clinics never deal with. A busy practice rarely has room for that, and some health systems discourage it. More on that here.
How to choose who writes yours
A few questions will tell you most of what you need to know:
- Will a physician read all of my records, or just a summary?
- If my case isn't supportable, will you tell me before I pay for the letter?
- Is the price stated up front, and does it change by condition?
- Who signs the letter, and what are their credentials?
- If something needs correcting, how is that handled?
How it works at Flat Rate Nexus
Everything happens online. There's no exam and no appointment. A physician reviews your records and writes the opinion.
- $549 total, any condition. A $149 deposit when you start, and $400 when your letter is ready. See pricing.
- If we can't support your claim, you get the $149 back in full, and you're never charged the $400.
- Most letters are ready within 14 days.
- We don't currently serve veterans in Oregon or Utah.
If you're not sure your case needs a letter at all, that's a fine place to start. Send us your records and we'll tell you honestly what we see.
How we got these numbers
- Source. Board of Veterans' Appeals decisions issued from 2021 through 2025, 295,756 in all, from the decisions the Board makes publicly available. Our set doesn't include every decision the Board issued in those years, so every number here means "in the decisions we reviewed."
- What we counted. Each service-connection issue the Board decided in the order section of a decision, one condition at a time. A decision that ruled on three conditions counts three times. Remands (claims sent back for more work) and withdrawn issues are left out. For these issues the Board either grants or denies; "granted in part" didn't occur.
- Grant rate. Granted issues divided by all decided issues for that condition.
- "With a private medical opinion." The Board's discussion of that condition mentions an opinion from a doctor or clinician outside the VA, whether or not the Board agreed with it. VA exams, and outside opinions the VA itself requested, are not counted as private.
- "The Board relied on it." In a granted issue, the Board used plain words such as "probative," "persuasive," or "great weight" about the private opinion. We report the lowest count we could confirm, so the real number is likely higher.
- Checking our work. We read random samples of decisions by hand. Our test for whether a private opinion was present was right 23 of 25 times when it said yes and 25 of 25 when it said no. Our count of the Board relying on an opinion was right 98 of 115 times. Every quote on this page was checked word for word against the decision it came from.
- Limits. Unusual wording can slip past a text search, so counts are floors. The Board is the appeal level and doesn't reflect how regional offices decide claims. And a higher grant rate alongside private opinions is an association, not proof that the opinion caused the result.
Guides by condition: Sleep apnea · Tinnitus · PTSD · Migraines · Back pain · GERD