The invoice a medical expense claim rests on

Two obligations, one to furnish and one on request

The substantiation paragraph does two separate things, and separating them is the fastest way to read it.

The first is unconditional. In connection with a claim, the taxpayer has to furnish the name and address of each person to whom payment for medical expenses was made, and the amount and date of the payment in each case. Where payment was made in kind, that fact has to be reflected.

The second is conditional and considerably more demanding. Claims have to be substantiated, when requested, by a statement or itemised invoice from the individual or entity to which payment was made.

That document has to show the nature of the service rendered, and to or for whom it was rendered. Where the expense is something other than a service, it has to show the nature of that item of expense, for whom it was incurred, and for what specific purpose, together with the amount paid and the date of payment.

The paragraph then leaves the list open: substantiation may also require such other information as is deemed necessary. So the itemised statement is a floor rather than a complete specification of what can be asked for.

This site does not give tax advice, and nothing here says what any reader should keep or claim. What follows describes what the published rule asks for.

Why a payment receipt is the wrong document

The document the regulation describes has four features a payment receipt generally lacks.

It comes from the payee. A statement or itemised invoice from the individual or entity to which payment was made is not the same as a confirmation produced by a card network or a bank.

It describes the service. A receipt shows an amount and a date; the regulation asks what was rendered.

It identifies the recipient of the service, meaning to or for whom it was rendered. That is a different fact from who paid.

And for anything that is not a service, it asks for the specific purpose. A line item naming a product with no stated purpose does not answer that.

A separate article on this site sets out what payment receipts are actually required to contain, which is a short list about amounts, dates, terminals and partial account numbers. None of the four features above is on it, and no payment rule obliges a seller to produce a document that has them.

The standard the expense itself has to meet

The regulation also states the substantive test the document is being asked to evidence, and it is stricter in tone than the statutory definition alone.

Deductions for expenditures for medical care are to be confined strictly to expenses incurred primarily for the prevention or alleviation of a physical or mental defect or illness.

The regulation gives a counter-example rather than a definition: an expenditure which is merely beneficial to the general health of an individual, such as an expenditure for a vacation, is not an expenditure for medical care.

That distinction between treating a defect or illness and improving general health is what a description of the nature of the service is being used to test. An invoice that names a product but says nothing about purpose leaves the question open.

The regulation lists what payments for medical care include, running through hospital services, nursing services, medical, laboratory, surgical, dental and other diagnostic and healing services, X-rays, medicine and drugs, artificial teeth or limbs, and ambulance hire.

The statutory limitation on medicine and drugs, and the definition of a prescribed drug, are covered in the sibling article built on the statute rather than restated here.

Whose expense, and when the status has to exist

One paragraph answers a question that comes up whenever a household buys care for more than one person.

Where medical expenses are for the care of a person who is the taxpayer's spouse or dependent, the deduction is allowable if that status exists either at the time the medical services were rendered, or at the time the expenses were paid.

The regulation illustrates the point in both directions: a payment made after a marriage for services rendered before it, and a payment made for services rendered to someone who became a spouse only later.

Because the status can be tested at either of two moments, the document has to establish both of them. The date of payment and the date the service was rendered are separate fields, and the regulation asks for the date of payment in the unconditional obligation and the nature of the service in the conditional one.

For a household buying in a cash-pay category, that is a practical point about what to ask a seller for. A record that fixes the payment date but not the service date answers only half the question the rule asks.

Reimbursement arriving late

A separate paragraph deals with a sequence that is common where a claim is made and money arrives afterward.

Where reimbursement, from insurance or otherwise, for medical expenses is received in a taxable year after a year in which a deduction was claimed on account of those expenses, the reimbursement has to be included in gross income in that later year to the extent attributable to, and not in excess of, deductions allowed for any prior taxable year.

The mirror image is also stated. If no medical expense deduction was taken in the earlier year, the reimbursement received later for that earlier expense is not includible in gross income.

The regulation then gives rules for attributing a reimbursement to a prior year's deduction, so that the aggregate result matches what it would have been had the reimbursement arrived in the year the expenses were paid.

That paragraph carries worked examples computed under limitations that the regulation itself identifies as applicable to taxable years beginning before or after dates in the early nineteen-sixties. None of those figures is reproduced here, and no current-year figure is asserted anywhere in this article, because the amounts in the examples describe a rule that has since changed.

The published guidance states the year-of-payment side of the same principle plainly: only amounts paid during the tax year for which no insurance or other reimbursement was received can be included. Anything about a particular filing position belongs with a tax adviser rather than with a comparison site.

Sources

Each document below is named as it names itself, with the date printed on that document rather than the day it was read.

1. Title 26 Code of Federal Regulations Section 1.213-1, Medical, dental, etc., expenses — read at paragraph (h), Substantiation of deductions; paragraph (e)(1), the definition of medical care and the general-health counter-example; paragraph (e)(3), status as spouse or dependent; and paragraph (g), Reimbursement for expenses paid in prior years. Paragraph letters (a) through (h) were enumerated to confirm the section was served in full — Electronic Code of Federal Regulations, Office of the Federal Register, November 1960
2. Publication 502 (2025), Medical and Dental Expenses, for use in preparing 2025 returns — read at What Are Medical Expenses and How Do You Treat Reimbursements — Internal Revenue Service, January 2025