Understanding Aadhaar Number Format
Aadhaar Number Structure
An Aadhaar number is a 12-digit unique identifier with a specific format. Learn more about what is an Aadhaar number and its importance in India.
- Digits 1-11: Randomly generated numbers
- Digit 12: Checksum digit calculated using the Verhoeff algorithm
The Verhoeff Algorithm
The Verhoeff algorithm is used to generate and validate the checksum digit. This algorithm helps detect common errors in the Aadhaar number, such as single-digit mistakes and transposition errors. When you use our Aadhaar validator, it applies this algorithm to verify the checksum.
Key Features of the Aadhaar Format
- Always 12 digits long
- First digit is never zero
- No alphabets or special characters
- Last digit is a checksum calculated using Verhoeff algorithm
Why Format Matters
Understanding the Aadhaar number format is relevant for:
- Building validation logic into forms and data pipelines
- Maintaining data integrity in databases
- Catching transcription errors before they reach UIDAI authentication
- Implementing a first-pass check in KYC workflows
Note: format validation confirms a number is structurally plausible, not that it has been issued by UIDAI or belongs to a real person. A number can pass the checksum and still be fictitious. For identity verification, use UIDAI’s official authentication services.
See how businesses use Aadhaar validation for practical use cases.
Using Our Validator
Our Aadhaar Check tool uses this understanding of the Aadhaar format to provide quick and accurate validation. It checks both the format and the checksum to ensure the number's validity. For a step-by-step guide, see how to validate an Aadhaar number.
Privacy and Compliance
When working with Aadhaar numbers, it's important to understand the legal requirements and privacy considerations. Read our guide on privacy and legal considerations when using Aadhaar data to ensure your implementation is compliant with Indian data protection laws.