Aadhaar Number Validator
Validate Aadhaar number format using the official Verhoeff checksum.
Written by Anil Gautam · Updated
How does the Verhoeff checksum catch a mistyped Aadhaar number?
The twelfth digit of an Aadhaar number is a check digit, calculated from the first eleven with a scheme published by the Dutch mathematician Jacobus Verhoeff in 1969. Reading your digits from right to left, the tool scrambles each one with a permutation that depends on its position and combines the results using a multiplication table built on the symmetries of a pentagon. A correctly formed number always ends the calculation at zero; any other result means at least one digit is wrong.
This design catches every single mistyped digit and every swap of two neighboring digits, such as 47 keyed in as 74. Simpler mod-10 checks miss some swaps: the Luhn check on bank cards gives 09 and 90 the same result. Two or more separate mistakes in one number can occasionally cancel out, so a number with several typos may still pass.
The sample the page opens with, 2345 6789 0123, fails this test. It has 12 digits and starts with 2, yet its final 3 does not match the first eleven digits, so the result card turns red.
What do the different error messages mean?
The tool runs three checks in order and reports the first failure. It first deletes spaces, hyphens and anything else that is not a digit, so 2345 6789 0123 and 2345-6789-0123 read the same. If the remaining count is not 12, the message says how many digits it found, which shows at once whether one was dropped or typed twice. Next comes the first digit: issued Aadhaar numbers start with 2 to 9, so a leading 0 or 1 is refused before any arithmetic. A number that clears both steps reaches the checksum, and a pass shows it regrouped into three blocks of four.
The input box holds at most 14 characters, enough for 12 digits plus two separators. Paste the bare number, since a label such as "Aadhaar:" copied along with it uses up that space before most of the digits arrive.
Which Aadhaar-related numbers will this tool reject?
Some other numbers on Aadhaar letters and cards fail here. The Virtual ID (VID) is 16 digits long and is generated for use in place of your Aadhaar number during authentication, so the tool rejects it with a count of 16. A masked Aadhaar shows only the last four digits, with the rest replaced by X, which leaves too little to check. The enrolment ID on an acknowledgment slip is much longer and fails on length as well.
For everyday use, treat the tool as a typo filter. When you enter employee or customer numbers into a payroll sheet or KYC form, running each one here first catches a mistyped or swapped digit before submission. For a PAN on the same form, the PAN Card Validator checks the pattern and decodes the holder type.