Brazilian CNH number validation rules and check digits
The CNH number has 11 digits: a 9-digit base and 2 check digits, computed in modulo 11 like the CPF, but with one important difference, the second check digit depends on the outcome of the first. This page works through the full calculation with a number that triggers both adjustment rules at once, the case that most confuses anyone trying to reimplement the validation from scratch.
The 9-to-1 weighted sum gives 165, remainder 0, first digit 0 with no overflow; the 1-to-9 weighted sum gives 285, remainder 10, which the second calculation's own rule turns into 0.
A first remainder of 10 triggers the adjustment of 2; a second remainder of 0 minus the adjustment goes negative and adds 11, closing at 9. This is the calculation that exposes both formula exceptions on the same base.
The two-digit calculation closes on 11, a mathematically valid result, but the final number of eleven repeated ones is rejected by a separate filter outside the modulo-11 formula.
No. It only follows the mathematical format used by form validators.
When the remainder of the first calculation (weights 9 to 1) is 10, the first digit becomes 0 and an adjustment of 2 is subtracted from the second calculation's result (weights 1 to 9); if that subtraction goes negative, 11 is added back to bring the result into the 0-to-9 range.
Not in this algorithm: the second digit is only complete once you know whether the first one overflowed the 0-to-9 range, because that exact result decides whether an adjustment of 2 enters the second calculation; treating the two as independent produces the wrong digit in a share of cases.
This text describes the calculation this generator implements, the widely documented two-digit modulo-11 scheme used across CNH generators and validators; there is no confirmation that it matches the official internal algorithm used by the issuing authority, so treat it as the tool's mechanism, not a published standard.
No, the calculation only confirms arithmetic consistency between the 9-digit base and the 2 check digits; it does not query the driving record, category, validity, point balance or any suspension status with the licensing authority.
Generation happens locally in the browser. Analytics receives only action, status, type and format, never the generated CNH.