The Letter of Medical Necessity

A Letter of Medical Necessity (LMN) is a short written statement from a licensed clinician saying that a specific product or service is medically necessary to treat or manage a specific condition. It is the document that turns ordinary spending into qualified medical spending.

How it works

The U.S. tax code (IRS §213(d)) lets money spent on medical care be paid with pre-tax dollars from an HSA or FSA. Many things that genuinely support health — in-home help after surgery, balance and fall-prevention work, certain equipment — aren’t automatically on the approved list. An LMN documents the medical necessity so those expenses can qualify. Your HSA/FSA administrator still makes the final call; the LMN is the evidence that supports it.

In practice: After a hip replacement, a 71-year-old needs eight weeks of in-home help with bathing, mobility, and getting to PT. With an LMN on file documenting that this care is necessary for her recovery, those hours can be paid with pre-tax HSA dollars instead of after-tax cash.

Source: Internal Revenue Code §213(d), which defines “medical care.” An LMN documents eligibility; it does not guarantee reimbursement — your plan administrator determines that.

This page is education, not tax, legal, or medical advice. Whether a specific expense qualifies depends on your situation, your plan, and a clinician’s determination — and the rules change. Talk to a tax advisor and your benefits administrator about your own case.