How is an Aadhaar number structured?

An Aadhaar number is exactly twelve digits. The first eleven digits are the identifier and the twelfth is a check digit calculated from them using the Verhoeff algorithm. By UIDAI convention the number never begins with 0 or 1, so the first digit is always between 2 and 9. There is no embedded personal information — unlike a PAN, the digits do not encode name, date of birth, or location; the number is randomly assigned.

Can this tool tell me if an Aadhaar is real or belongs to someone?

No. It confirms the number has the correct length, a valid leading digit, and a consistent Verhoeff check digit — which catches typos and fabricated-looking numbers. But it cannot confirm the Aadhaar was actually issued or that it belongs to a particular person. Only UIDAI, through its official authentication and verification services and with the holder’s consent, can do that. Any tool claiming to “verify” an Aadhaar identity offline is overstating what is possible.

What is the Verhoeff check digit and why does it matter?

The Verhoeff algorithm is a checksum scheme that produces a single check digit designed to catch the most common human data-entry errors — particularly single wrong digits and swaps of two adjacent digits. UIDAI uses it for the last digit of every Aadhaar. Because the algorithm is public, this page can recompute the check digit in your browser and confirm a number is internally consistent, without contacting any server. It is the reason an Aadhaar can be validated offline while a PAN cannot.

Is my Aadhaar number sent anywhere when I use this tool?

No. The entire check runs inside your browser using JavaScript on this page. The number you type is never transmitted to our servers or any third party, is not logged, and is not stored after you leave the page. Page analytics record only that the page was viewed, never the contents of the input. The tool continues to work even if you disconnect from the internet after the page loads, which you can verify in your browser’s network tab.

What does the masked Aadhaar form mean and when should I use it?

Masking hides the first eight digits and keeps only the last four, shown as XXXX XXXX 1234. UIDAI recommends this pattern whenever an Aadhaar must be displayed or referenced, because the last four digits are usually enough to identify a record while the hidden digits protect the holder. Use the masked form in support tickets, internal notes, screenshots, printed documents, and logs — anywhere you do not strictly need the full number.

Why does a twelve-digit number sometimes still show as invalid?

Length alone does not make an Aadhaar valid. If the number starts with 0 or 1 it is rejected because UIDAI does not issue such numbers. If all twelve digits are present and the leading digit is fine but the number still fails, the Verhoeff check digit did not match — meaning at least one digit is wrong, most often a typo or a transposition. Re-checking the number against the source usually resolves it.

Is it legal to handle or mask Aadhaar numbers like this?

Validating a number’s format and producing a masked version for your own legitimate records is a routine, privacy-protective operation, and masking is exactly what UIDAI encourages for display. What the law restricts is storing, sharing, or publishing full Aadhaar numbers without authority and safeguards. Because this tool runs entirely in your browser and stores nothing, it is designed to help you handle Aadhaar data more safely, not less. Always have a legitimate reason and consent before handling anyone else’s Aadhaar.

Is this tool free? Will it ever be paid?

The single-number check and mask on this page will always be free with no rate limit. We may later add bulk validation and masking with CSV export — useful for teams cleaning KYC datasets before upload — behind the Samastam Pro subscription once it launches, but the individual check here stays free with no signup and no ads.

Lookup

Aadhaar Validator & Masking Tool

Check any Indian Aadhaar number for correct format and a valid Verhoeff check digit, and get a safe masked form to share. Free, 100% in-browser, no signup, no ads — your number never leaves your device.

By the Samastam teamLast updated 2026-07-19

Enter Aadhaar number

Try:

Enter a twelve-digit Aadhaar number above. Its format and Verhoeff check digit are validated here automatically — entirely in your browser. The number is never sent anywhere.

An Aadhaar number is the twelve-digit identity number the Unique Identification Authority of India (UIDAI) issues to residents. Its twelfth digit is a Verhoeff check digit computed from the first eleven, which means a correctly typed Aadhaar can be validated mathematically — offline, with no lookup. Paste one below to check its format and check digit, and to produce a masked version (XXXX XXXX 1234) that is safe to put in a support ticket or screenshot. Everything runs in your browser; the number is never sent anywhere.

What this is and why it matters

The Aadhaar number is the most widely used identity number in India, held by well over a billion residents and quoted for everything from opening a bank account to receiving a subsidy. Because it is requested so often, it is also mistyped, misprinted, and mis-stored constantly — on forms, in spreadsheets, in customer databases, and in support tickets. A single transposed digit in a KYC record can break a bank linkage, delay a benefit, or cause a payment to fail. Being able to check that a twelve-digit number is at least internally consistent, before it is saved or acted upon, prevents a whole category of avoidable errors.

Unlike a PAN, whose check-digit formula the Income Tax Department has never released, the Aadhaar number carries a check digit computed with the Verhoeff algorithm — a published scheme designed to catch the most common human errors, especially single-digit mistakes and adjacent transpositions. The first eleven digits are the identifier and the twelfth is derived from them. This tool recomputes that check digit in your browser and compares it, so a number with a typo is flagged immediately, without any call to a government server. It also applies the two structural rules UIDAI follows: the number is exactly twelve digits, and it never begins with 0 or 1.

Just as important is what this tool deliberately does not claim. A passing check means the number is well-formed and its check digit is consistent — it does not mean the Aadhaar has been issued to a real person or is currently active. Only UIDAI, through its authentication and verification services, can confirm that, and doing so requires consent and is not something any offline page can or should attempt. The second job of this tool is privacy: it produces a masked form that hides the first eight digits, so you can reference an Aadhaar in a ticket, a screenshot, or a log without exposing the full number. Handling Aadhaar data carelessly carries real legal and security consequences, and masking is the simplest habit that reduces that risk.

Examples and use cases

Catching a transposed digit in a bank KYC form

A Kolkata bank branch keys in a customer’s Aadhaar during account opening and the system later rejects the Aadhaar-bank linkage. Running the captured number through this tool shows the Verhoeff check digit fails — two adjacent digits had been swapped during data entry. The Verhoeff algorithm is specifically good at catching exactly this kind of transposition, so the error is spotted in seconds rather than surfacing days later as a failed DBT credit.

Masking an Aadhaar before raising a support ticket

A fintech support agent in Hyderabad needs to reference a user’s Aadhaar in an internal ticket. Instead of pasting the full twelve digits — a privacy and compliance risk — they run it through this tool and copy the masked form, XXXX XXXX 2859. The ticket now carries just enough to identify the record without exposing the full number, following the UIDAI-recommended masking pattern.

Screening a spreadsheet of Aadhaar numbers before upload

An NGO in Jaipur maintains beneficiary records and must upload Aadhaar-linked data for a scholarship scheme. Before uploading, a volunteer checks a sample of the numbers here and finds several that are only eleven digits and one that starts with a 1 — both structurally impossible. Fixing these before submission avoids a batch rejection that would have delayed disbursement for every beneficiary in the file.

Verifying a self-typed Aadhaar on an online form

A student in Lucknow filling a government scholarship portal is unsure they typed their Aadhaar correctly. They paste it into this tool, see that the format and check digit both pass, and proceed with confidence — knowing a mistyped number would have failed the Verhoeff check. They still understand this does not “verify” their identity; it only confirms the digits are self-consistent.

Explaining why an Aadhaar was rejected as invalid

A small business in Surat collects an Aadhaar from a vendor for records and their software flags it invalid. The owner pastes it here and the tool reports a failed check digit, making clear the problem is a typo in the number itself, not a software bug. They ask the vendor to re-share the number, and the corrected one passes — turning a confusing rejection into a two-minute fix.

Frequently asked questions

How is an Aadhaar number structured?: An Aadhaar number is exactly twelve digits. The first eleven digits are the identifier and the twelfth is a check digit calculated from them using the Verhoeff algorithm. By UIDAI convention the number never begins with 0 or 1, so the first digit is always between 2 and 9. There is no embedded personal information — unlike a PAN, the digits do not encode name, date of birth, or location; the number is randomly assigned.
Can this tool tell me if an Aadhaar is real or belongs to someone?: No. It confirms the number has the correct length, a valid leading digit, and a consistent Verhoeff check digit — which catches typos and fabricated-looking numbers. But it cannot confirm the Aadhaar was actually issued or that it belongs to a particular person. Only UIDAI, through its official authentication and verification services and with the holder’s consent, can do that. Any tool claiming to “verify” an Aadhaar identity offline is overstating what is possible.
What is the Verhoeff check digit and why does it matter?: The Verhoeff algorithm is a checksum scheme that produces a single check digit designed to catch the most common human data-entry errors — particularly single wrong digits and swaps of two adjacent digits. UIDAI uses it for the last digit of every Aadhaar. Because the algorithm is public, this page can recompute the check digit in your browser and confirm a number is internally consistent, without contacting any server. It is the reason an Aadhaar can be validated offline while a PAN cannot.
Is my Aadhaar number sent anywhere when I use this tool?: No. The entire check runs inside your browser using JavaScript on this page. The number you type is never transmitted to our servers or any third party, is not logged, and is not stored after you leave the page. Page analytics record only that the page was viewed, never the contents of the input. The tool continues to work even if you disconnect from the internet after the page loads, which you can verify in your browser’s network tab.
What does the masked Aadhaar form mean and when should I use it?: Masking hides the first eight digits and keeps only the last four, shown as XXXX XXXX 1234. UIDAI recommends this pattern whenever an Aadhaar must be displayed or referenced, because the last four digits are usually enough to identify a record while the hidden digits protect the holder. Use the masked form in support tickets, internal notes, screenshots, printed documents, and logs — anywhere you do not strictly need the full number.
Why does a twelve-digit number sometimes still show as invalid?: Length alone does not make an Aadhaar valid. If the number starts with 0 or 1 it is rejected because UIDAI does not issue such numbers. If all twelve digits are present and the leading digit is fine but the number still fails, the Verhoeff check digit did not match — meaning at least one digit is wrong, most often a typo or a transposition. Re-checking the number against the source usually resolves it.
Is it legal to handle or mask Aadhaar numbers like this?: Validating a number’s format and producing a masked version for your own legitimate records is a routine, privacy-protective operation, and masking is exactly what UIDAI encourages for display. What the law restricts is storing, sharing, or publishing full Aadhaar numbers without authority and safeguards. Because this tool runs entirely in your browser and stores nothing, it is designed to help you handle Aadhaar data more safely, not less. Always have a legitimate reason and consent before handling anyone else’s Aadhaar.
Is this tool free? Will it ever be paid?: The single-number check and mask on this page will always be free with no rate limit. We may later add bulk validation and masking with CSV export — useful for teams cleaning KYC datasets before upload — behind the Samastam Pro subscription once it launches, but the individual check here stays free with no signup and no ads.