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ISO 7064 Check Character Calculator

Enter a value and pick the ISO 7064 algorithm to compute its check character.

How it is calculated

Both modes run a recursive check over the characters from left to right. For MOD 11,10 (digits only) start with P = 10. For each digit d: S = (P mod 11) + d, then S = S mod 10, and if S is 0 it becomes 10; then P = (2 × S) mod 11. The check digit is (11 − P) mod 10, so it is always 0 to 9. The MOD 37,36 mode works the same way on the alphabet 0-9 and A-Z with modulus 36 and radix 37, and lower-case letters are upper-cased. The tool returns the check character and the full value with it appended. Leading zeros count, and spaces or hyphens are rejected, so strip them first.

Worked example

Value 0794 in MOD 11,10. Start P = 10. Digit 0: S = 10 + 0 = 10, so P = 20 mod 11 = 9. Digit 7: S = 9 + 7 = 16, mod 10 gives 6, so P = 12 mod 11 = 1. Digit 9: S = 1 + 9 = 10, which becomes 10, so P = 20 mod 11 = 9. Digit 4: S = 9 + 4 = 13, mod 10 gives 3, so P = 6. Check digit: (11 − 6) mod 10 = 5, so the full value is 07945.

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Common mistakes

  • Dropping leading zeros. 0794 gives check digit 5, while 794 gives 6, so the zero is part of the data.
  • Typing spaces or hyphens inside the identifier. The numeric mode accepts only digits and the alphanumeric mode only 0-9 and A-Z, so such input gives no result.
  • Using MOD 11,10 for an identifier that contains letters, or mixing up the two modes. The same value has different check characters under MOD 11,10 and MOD 37,36 (0794 gives 5 and J).
  • Entering a value that already includes its check digit and expecting a pass or fail answer. The tool always appends a new character, so enter the value without the check digit.
  • Assuming a matching check digit proves the number is real. It only catches typing mistakes; it does not show that the identifier is issued.

About this calculator

The ISO 7064 check character calculator appends a verification character to an identifier using one of the standard's algorithms: MOD 11,10 for purely numeric strings, or MOD 37,36 for alphanumeric strings (letters A–Z plus digits 0–9). Both work by processing the value digit by digit, applying a running modular calculation with a fixed radix, and deriving a single check character designed to catch the most common data-entry mistakes — a single mistyped character or two adjacent characters swapped (transposition).

ISO/IEC 7064 is the international standard behind check-digit schemes used in identifiers such as the International Standard Audiovisual Number (ISAN) and various national registration and organization codes, where a simple typo could otherwise route a document or payment to the wrong record. Software developers implementing ID validation, and standards or compliance teams use this calculator to verify that a generated identifier's check character is correct, or to compute the missing check character for a new one.

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Comments (1)

  • Editorial team

    This tool only appends a check character, but you can use it to verify an existing number: remove the last character, compute it for the rest, and compare. For 794623 in MOD 11,10, strip the 3, enter 79462 and the tool returns 3, so the number passes. Keep leading zeros and use the same algorithm the issuer used. Which identifier scheme are you checking?

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