Check digit validator (MOD10 / MOD11)
Validate check digits for free. Supports MOD10 and MOD11, shows the correct check digit, and cleans input automatically.
Result:
Calculate check digit
Enter base number (without check digit) and choose algorithm.
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How do check digits work?
Check digits are used in payment references, barcodes, and identification numbers to catch typing errors. Two common algorithms are MOD10 (Luhn) and MOD11.
MOD10 (Luhn)
- Start from the right (without check digit) and multiply every other digit by 2 and 1.
- Sum digit totals (9*2=18 → 1+8=9).
- Check digit = (10 - (sum % 10)) % 10.
MOD11
- Start from the right (without check digit) with weights 2,3,4,5,6,7 and repeat.
- R = sum % 11, check digit = 11 - R; 11 → 0, 10 → invalid check digit.