Barcode Check Digit Calculator

UPC-A Example: Coca-Cola

ISBN-10 Example: Programming Book

Python Implementation

def calculate_upc_check_digit(digits):
    """Calculate UPC/EAN check digit"""
    total = 0
    for i, digit in enumerate(digits):
        weight = 3 if i % 2 == 1 else 1
        total += int(digit) * weight
    
    remainder = total % 10
    return 0 if remainder == 0 else 10 - remainder

def calculate_isbn10_check_digit(digits):
    """Calculate ISBN-10 check digit"""
    total = sum(int(d) * (10 - i) for i, d in enumerate(digits))
    remainder = total % 11
    check_digit = 11 - remainder
    
    if check_digit == 10:
        return 'X'
    elif check_digit == 11:
        return '0'
    else:
        return str(check_digit)

JavaScript Implementation

function calculateUpcCheckDigit(digits) {
    let total = 0;
    for (let i = 0; i < digits.length; i++) {
        const weight = (i % 2 === 1) ? 3 : 1;
        total += parseInt(digits[i]) * weight;
    }
    
    const remainder = total % 10;
    return remainder === 0 ? 0 : 10 - remainder;
}

function calculateIsbn10CheckDigit(digits) {
    let total = 0;
    for (let i = 0; i < digits.length; i++) {
        total += parseInt(digits[i]) * (10 - i);
    }
    
    const remainder = total % 11;
    const checkDigit = 11 - remainder;
    
    if (checkDigit === 10) return 'X';
    if (checkDigit === 11) return '0';
    return checkDigit.toString();
}