What Is an NPI Number?
An NPI (National Provider Identifier) is a unique 10-digit number that identifies a U.S. health care provider or organization. It is the standard identifier under HIPAA, and health plans, including Medicare and Medicaid, require it on claims and other administrative transactions. The Centers for Medicare & Medicaid Services (CMS) assigns NPIs through a system called NPPES, and the number is meant to stay with a provider for good, even if their name, address or specialty changes.
Have an NPI, a name or an organization to look up? Use the free search below. Otherwise, read on for what an NPI is, who needs one, how the numbers are built, and what they do and do not tell you.
Provider information is based on publicly available NPPES data. An NPI does not indicate licensure, credentialing, network participation, or current practice status.
What an NPI is
HIPAA (the Health Insurance Portability and Accountability Act of 1996) required a standard unique identifier for health care providers. The NPI Final Rule, issued on January 23, 2004, adopted the NPI as that standard. Before it, providers typically had a different identifier for each health plan they billed.
An NPI has three defining traits:
- It is 10 digits long. Nine digits form the identifier and the tenth is a check digit.
- It carries no meaning. CMS calls it “intelligence-free”: the digits do not encode the provider's state, specialty or type.
- It is unique and lasting. Each number belongs to one provider or organization. CMS says it is expected to remain unchanged even if the provider changes their name, address or provider taxonomy (specialty classification).
CMS maintains the National Plan and Provider Enumeration System (NPPES), which assigns NPIs and stores the record for every one of them.
Who needs an NPI
A health care provider that is a HIPAA covered entity, for example one that bills a health plan electronically, must have an NPI and use it in standard transactions such as claims and eligibility checks. Other providers are allowed to get one, and many do, because Medicare, Medicaid and private health plans expect it. An NPI is also required for Medicare enrollment, although getting one does not replace the Medicare enrollment process.
NPIs are issued to individuals such as physicians, nurse practitioners and dentists, and to organizations such as hospitals, nursing homes and physician groups.
Individual (Type 1) vs organization (Type 2) NPIs
There are two kinds of NPI, and which one applies depends on who is being identified, not on the number itself.
| Attribute | Type 1 (individual) | Type 2 (organization) |
|---|---|---|
| Who it is for | Individual providers: physicians, nurse practitioners, dentists, and sole proprietors | Organizations: hospitals, nursing homes, physician groups, and a corporation or LLC an individual has formed |
| How many | One per individual | An organization can have more than one |
| Code in NPPES data | Entity type code 1 |
Entity type code 2 |
| Identified by | First name, last name and credential | Organization name |
A sole proprietor is treated as an individual, so they get a single Type 1 NPI. A health care provider who has incorporated, or formed an LLC, can have an NPI for themselves (Type 1) and another for the company (Type 2). Large organizations can also request separate NPIs for subparts such as distinct locations or business units when they need to bill separately. CMS leaves each organization to decide how to treat its subparts.
NPI format and the check digit
An NPI is exactly 10 digits: a nine-digit identifier followed by one check digit. CMS initially issued NPIs starting with a 1 or a 2, to keep them from colliding with other identifiers used on health ID cards. Beyond that, the digits mean nothing on their own.
The check digit exists to catch typing mistakes. It is calculated from the first nine
digits with the Luhn formula (the same “mod 10” method used for payment card
numbers), treating the number as if it had the prefix 80840 in front of
it. The prefix stands for health applications in the United States. Because it is not
part of the NPI, CMS's shortcut is to add the constant 24, which is what the prefix
contributes to the sum.
Worked example
CMS publishes 123456789 as its example nine-digit identifier. To find its
check digit:
- Double every second digit, starting from the rightmost of the nine.
- Add up the individual digits of every result, plus the constant 24.
- Subtract the total from the next multiple of ten. That is the check digit (0 if the total is already a multiple of ten).
| Digit | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|
| Doubled? | yes | no | yes | no | yes | no | yes | no | yes |
| Result | 2 | 2 | 6 | 4 | 10 | 6 | 14 | 8 | 18 |
| Digit sum | 2 | 2 | 6 | 4 | 1 | 6 | 5 | 8 | 9 |
The digit sums add up to 43. Adding the constant 24 gives 67. The next
multiple of ten is 70, and 70 − 67 = 3. The check digit is 3, so
the complete number is 1234567893.
A passing check digit is not proof that an NPI exists. It only shows the number is well formed. Most numbers that pass the test have never been assigned to anyone, and an assigned NPI can later be deactivated. Whether an NPI is real, and what it belongs to, can only be answered by looking it up in NPPES. Our NPI lookup tells you which of four things is true: the number is not 10 digits, it fails the check digit, it is well formed but not found, or it was found (active or deactivated).
NPI vs tax ID and other identifiers
Providers carry several numbers, and they are easy to confuse. Each answers a different question.
| Identifier | Issued by | What it identifies |
|---|---|---|
| NPI | CMS, through NPPES | A health care provider or organization, in HIPAA transactions |
| Tax ID (EIN, or SSN used as a TIN) | The IRS (EIN) or the Social Security Administration (SSN) | A taxpayer, for tax reporting. It says nothing about who provided care |
| State license number | A state licensing board | Authority to practice a profession in that state |
| DEA registration number | The Drug Enforcement Administration | Authority to prescribe or dispense controlled substances |
| Medicare or Medicaid enrollment | Medicare, or the state Medicaid program | Enrollment in that program. CMS notes an NPI does not enroll a provider in a health plan |
The practical difference between an NPI and a tax ID: the NPI identifies who provided the care, while the tax ID identifies who is taxed and paid. A group's providers each have their own NPI but typically bill under the group's tax ID, which is why a claim usually carries both.
What an NPI does not tell you
CMS is explicit that having an NPI does not ensure a provider is licensed or credentialed, does not guarantee payment by a health plan, and does not enroll the provider in a health plan. Beyond that, an NPPES record does not show:
- whether a provider is board certified;
- whether they accept new patients or take a particular insurance;
- whether they currently practice at the address listed.
The record is only as current as the provider keeps it. CMS requires covered providers to report changes to the information behind their NPI within 30 days, but the records are maintained by the providers themselves, so addresses and specialties can lag. NPPES also records deactivation and reactivation dates. For a deactivated NPI, CMS publishes only the number and the date it was deactivated. For anything that matters, such as credentialing or choosing a doctor, confirm with the state licensing board, the health plan, or the provider directly.
How to find an NPI number
- Search here. Our free NPI lookup finds a provider by NPI, name or organization, and you can narrow it by state. To search by specialty and location instead, use Provider Search.
- Use the official registry. The CMS NPI Registry is CMS's own search tool. It is free and updated daily.
- Ask the provider. An NPI is often printed on billing statements, referral forms and credentialing paperwork, and providers know their own number.
For a common name, add the state and choose “individual” or “organization” to cut the list down.
How to get an NPI
Getting an NPI is free. CMS describes three ways to do it:
- Complete the online application at nppes.cms.hhs.gov.
- Download the paper application form from CMS.gov.
- Authorize an employer or other trusted organization to obtain the NPI for you through bulk enumeration, also called Electronic File Interchange.
Once you have one, keep it current: report changes within 30 days. Updating NPPES does not automatically update Medicare enrollment records, so those need their own update.
Using NPIs in software
If your application accepts NPIs, checking the format and check digit before you use the number catches typos for free, with no network call. Here it is in JavaScript. We tested it against thousands of real NPIs and CMS's own example:
function isValidNpi(npi) {
if (!/^\d{10}$/.test(npi)) return false;
// CMS check digit: Luhn over "80840" + the first nine digits
const payload = '80840' + npi.slice(0, 9);
let sum = 0;
for (let i = payload.length - 1, dbl = true; i >= 0; i--, dbl = !dbl) {
let d = Number(payload[i]);
if (dbl) { d *= 2; if (d > 9) d -= 9; }
sum += d;
}
return (10 - (sum % 10)) % 10 === Number(npi[9]);
}
isValidNpi('1234567893'); // true
isValidNpi('1234567894'); // false (typo in the check digit)
Remember the limit from above: this proves an NPI is well formed, not that it is assigned. To confirm a number exists, and to get the provider's name, specialty and practice address, you need the data itself. CMS publishes NPPES as a monthly full file and weekly updates. NPILayer keeps a local, normalized copy and serves it through a REST API, so a lookup is one request:
curl -H "Authorization: Bearer YOUR_API_KEY" \ "https://api.npilayer.com/v1/providers/1234567893"
See the Healthcare Provider API overview, the provider endpoint documentation, or get a free API key.
Frequently asked questions
Is an NPI number free?
Yes. CMS assigns NPIs at no charge, and searching the NPI Registry is free too.
Does an NPI expire or change?
CMS describes the NPI as a lasting identifier that is expected to stay the same when a provider's name, address or specialty changes. An NPI can be deactivated, though, and NPPES records deactivation and reactivation dates.
Can two providers share an NPI?
No. Each NPI is unique to one provider or organization, and an individual can have only one. An organization, on the other hand, can have several.
Is an NPI the same as a license number?
No. A license number comes from a state licensing board and shows authority to practice. An NPI comes from CMS and only identifies the provider. Having an NPI does not show that someone is licensed.
Are NPI records public?
Yes. CMS discloses the NPPES data that the Freedom of Information Act allows, through the NPI Registry and downloadable data files, at no charge. It has done so since September 2007.
Does a valid NPI mean the provider is in my insurance network?
No. NPI enumeration is separate from network participation. Ask your insurer or the provider to confirm.
Sources
This guide is based on CMS documentation. NPPES data changes, so check the CMS pages for the latest rules.
- The National Provider Identifier (NPI) Fact Sheet, CMS, December 2024
- Requirements for NPI and NPI Check Digit, CMS, January 23, 2004
- National Provider Identifier Standard (NPI), CMS
- Unique Identifiers FAQs, CMS
- NPPES Data Dissemination, CMS
- NPPES and the NPI Registry
NPILayer is not affiliated with CMS or the U.S. government.