Checking an Aadhaar number's format catches the most common data entry mistakes instantly, without needing to contact UIDAI. This guide walks through validating the format and understanding what that check does and doesn't tell you.
What You Need
- The 12-digit Aadhaar number you want to check, with or without spaces
- Access to the Aadhaar Validator for instant checking, or a way to manually compute the Verhoeff checksum
Step 1: Confirm the Number Has Exactly 12 Digits
Strip any spaces or hyphens from the number and count the digits — a valid Aadhaar number is always exactly 12 digits long, no more and no fewer. If your number has a different digit count after removing separators, it's already invalid before any checksum is even applied.
Step 2: Understand the Verhoeff Checksum
Aadhaar numbers use the Verhoeff algorithm for their final check digit — a more robust method than simple weighted-sum checksums, since it catches all single-digit errors and most cases where two adjacent digits have been swapped. The algorithm works through multiplication and permutation tables rather than a simple linear formula, which is why manual verification is impractical and a validator tool is the practical approach.
Step 3: Run the Number Through a Validator
Enter the 12-digit number into the Aadhaar Validator. The tool strips any spaces automatically, confirms the digit count, and applies the Verhoeff checksum to tell you immediately whether the number is structurally valid.
Step 4: Interpret a Failing Result
If the check fails, the most likely cause is a single mistyped digit or a transposition of two adjacent digits — both of which the Verhoeff algorithm is specifically designed to catch. Compare the number carefully against the original Aadhaar card or downloaded e-Aadhaar PDF to find and correct the discrepancy.
Step 5: Understand What a Passing Result Does and Doesn't Mean
A passing checksum confirms the number is correctly formed according to UIDAI's algorithm. It does not confirm the number has actually been issued, is currently active, or belongs to the person presenting it. Real verification of those facts requires checking through UIDAI's official verification channels — a website format check is a first-line filter for typos, not a substitute for actual identity verification.
Step 6: Use Masked Aadhaar When Sharing the Number
If you need to display or share an Aadhaar number but don't need to reveal it in full, use the masked format — showing only the last 4 digits with the first 8 replaced by Xs (XXXX XXXX 2346). The Aadhaar Formatter generates this format automatically from a full number, following UIDAI's recommended privacy practice.
Common Mistakes to Avoid
Treating a passing checksum as identity verification. Format validation and real identity verification are different things — don't conflate them in a KYC or compliance context.
Not stripping spaces before counting digits. Aadhaar numbers are commonly written with spaces in groups of four; strip these before checking the digit count.
Sharing the full number when masked would suffice. Default to the masked format whenever full visibility isn't specifically required.
Assuming all 12-digit numbers are Aadhaar-shaped. Other 12-digit numbers (like some barcode formats) won't pass the Aadhaar-specific Verhoeff checksum, and vice versa — the check is specific to Aadhaar's exact algorithm.
Key Terms
- Aadhaar — India's 12-digit biometric identity number, issued by UIDAI and validated using the Verhoeff algorithm.
- PAN — India's tax-specific identifier, a separate 10-character alphanumeric format from Aadhaar.
- Masked Aadhaar — a privacy-preserving display format showing only the last 4 digits of an Aadhaar number.