International · Validation
India Aadhaar number validator.
Check a 12-digit Aadhaar number against the Verhoeff check digit its last digit carries, plus the rule that issued numbers start with 2 to 9. Everything runs in your browser.
How it works: the first 11 digits are run through Verhoeff's 1969 dihedral-group algorithm to produce the 12th digit. If the digit you typed doesn't match, the number has a typo.
Inputs
Result
Enter an Aadhaar number and press Check.
How the Aadhaar check digit works
An Aadhaar number is 12 digits: 11 digits followed by a check digit. The check digit comes from the Verhoeff algorithm, published by Dutch mathematician Jacobus Verhoeff in 1969. Unlike a simple weighted sum, it is built on the dihedral group D5, so it catches every single-digit error and every swap of two adjacent digits.
| Step | What happens |
|---|---|
| 1 | Write the 12 digits and read them right to left |
| 2 | Start with a running value c = 0 |
| 3 | For each digit at position i, permute it with row (i mod 8) of Verhoeff's permutation table, then combine it with c using the D5 multiplication table |
| 4 | The number is valid if and only if c ends at 0 |
Issued Aadhaar numbers also begin with a digit from 2 to 9, so this tool rejects numbers starting with 0 or 1 before running the checksum.
Checksum check only, not a UIDAI lookup
A passing result means the digits are internally consistent. It does not confirm the number was issued to anyone. Only UIDAI can confirm that, through its own verification services.
Sources
Verhoeff, J., Error Detecting Decimal Codes, Mathematical Centre Tracts 29, Amsterdam, 1969 (algorithm and tables, summarised at Wikipedia: Verhoeff algorithm). Aadhaar's 12-digit format, first-digit rule and use of Verhoeff: Wikipedia: Aadhaar.
Checksum only — not a UIDAI lookup
This tool checks the Verhoeff checksum entirely in your browser. It does not query UIDAI, and a checksum-valid result is not proof the number was ever issued. Nothing you type is transmitted, stored, or logged.