Check whether a 12-digit Aadhaar number has a valid format and passes the official Verhoeff checksum used by UIDAI.
| Position | Digits | Meaning |
|---|---|---|
| 1 | 1 digit | Cannot be 0 or 1 (UIDAI rule) |
| 2–11 | 10 digits | Random sequence assigned by UIDAI |
| 12 | 1 digit | Verhoeff check digit |
A decimal check-digit algorithm developed by Jacobus Verhoeff in 1969 that detects all single-digit and adjacent-transposition errors.
Aadhaar's 12-digit format chose Verhoeff over Luhn for stronger error detection - useful when numbers are read out or typed manually.
A valid checksum only proves the number is well-formed. It does not confirm the Aadhaar is real or active - only UIDAI can verify that.
Aadhaar is a 12-digit unique identification number issued by the Unique Identification Authority of India (UIDAI) to every resident of India. Launched in 2009 under the chairmanship of Nandan Nilekani, the Aadhaar programme has enrolled over 1.38 billion individuals as of 2024, making it the world's largest biometric identity system. The number is not random - its final digit is a checksum calculated using the Verhoeff algorithm, a mathematical method that detects single-digit errors and all two-digit transposition errors.
Invented by Dutch mathematician Jacobus Verhoeff in 1969, the Verhoeff algorithm uses three tables - a multiplication table (dihedral group D5), a permutation table, and an inverse table - to generate a check digit. UIDAI adopted this algorithm because it catches more common data-entry mistakes than simpler methods like Luhn (used in credit cards). When validating an Aadhaar number, the algorithm processes all 12 digits and the result should equal zero for a valid number. The first digit can never be 0 or 1.
This validator checks three things: that the number is exactly 12 digits, that it does not start with 0 or 1, and that it passes the Verhoeff checksum. It does NOT connect to UIDAI servers or confirm whether the number belongs to a real person - only UIDAI's official Aadhaar verification portal can do that. Use this tool to catch formatting errors before submitting forms to government portals, banks, or insurance companies where Aadhaar is mandatory for KYC.