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Aadhaar

General

Indian Biometric Identity Number

A unique 12-digit identity number issued by UIDAI to Indian residents, linked to biometric and demographic data. Used widely for identity verification, KYC, and government service delivery.

Definition

Aadhaar is a 12-digit unique identity number issued by the Unique Identification Authority of India (UIDAI) to residents of India, linked to an individual's biometric data — fingerprints and iris scans — along with basic demographic details. Since its rollout, Aadhaar has become the most widely held identity document in India, used for identity verification, government subsidy delivery, and KYC compliance across banking and financial services.

Unlike PAN, which is specifically a tax identifier issued by the Income Tax Department, Aadhaar is a general-purpose identity number issued by UIDAI and verified through biometric matching rather than purely documentary checks. The two numbers are commonly linked (PAN-Aadhaar seeding) but remain functionally distinct systems.

Formula

Aadhaar numbers use the Verhoeff algorithm for their check digit — a checksum method more robust than simple weighted-sum approaches, capable of detecting all single-digit errors and most transposition errors (where two adjacent digits are swapped). The algorithm works by mapping digits through multiplication and permutation tables derived from the mathematics of the dihedral group D5, rather than a simple linear formula.

Worked Example

An Aadhaar number entered as a continuous 12-digit string, such as 234123412346, is conventionally displayed grouped into three sets of four digits: 2341 2341 2346.

If only partial visibility is needed — for instance, on a document being shared with a third party — UIDAI's masked format replaces the first 8 digits: XXXX XXXX 2346.

Key Things to Know

  • 12 digits, grouped in 4s: the standard display format is three groups of four digits, separated by spaces.
  • Verhoeff checksum, not simple weighted-sum: Aadhaar's check digit algorithm catches more error types than the simpler checksums used by PAN-style alphanumeric IDs.
  • Masked Aadhaar protects privacy: showing only the last 4 digits is the UIDAI-recommended format for situations where the number must be displayed but full exposure isn't necessary.
  • Distinct from PAN: Aadhaar is a general identity number from UIDAI; PAN is a tax-specific identifier from the Income Tax Department. They're linked, not interchangeable.

Related Terms

PANPermanent Account NumberUPIUnified Payments InterfaceGSTGoods and Services Tax

Frequently Asked Questions

No. Aadhaar is a 12-digit identity number issued by UIDAI, linked to biometric data (fingerprints and iris scans) and used broadly for identity verification across government services. [PAN](/glossary/pan/) is issued by the Income Tax Department specifically for tax and financial transactions. The two are linked under the mandatory PAN-Aadhaar seeding requirement, but they serve different purposes.
A masked Aadhaar shows only the last 4 digits of the number, with the first 8 digits replaced by Xs (displayed as XXXX XXXX 1234). UIDAI recommends this format whenever an Aadhaar number needs to be shared or printed but full visibility isn't required, such as on a document submitted to a third party.
Aadhaar numbers use the Verhoeff algorithm, a checksum method that detects all single-digit errors and most adjacent transposition errors. Unlike simpler weighted-sum checksums, Verhoeff uses lookup tables based on the mathematics of the dihedral group, making it more robust against common typing mistakes.
Aadhaar is mandatory for certain government welfare schemes and subsidies, and is commonly requested for KYC (Know Your Customer) verification by banks and financial institutions. However, the legal requirement varies by transaction type and has been shaped by several Supreme Court rulings on privacy and mandatory linkage.
UIDAI recommends using masked Aadhaar (showing only the last 4 digits) whenever possible, and avoiding sharing your full Aadhaar number or a photocopy without a clear, stated purpose. Aadhaar-linked biometric and demographic data is sensitive, so minimising exposure of the full number reduces misuse risk.