Editing Check digit (section)

=== UPC, EAN, GLN, GTIN, numbers administered by GS1 ===

The final digit of a [[Universal Product Code]], [[International Article Number]], [[Global Location Number]] or [[Global Trade Item Number]] is a check digit computed as follows:<ref name=UCCOUNCIL>{{cite web|url=http://www.uc-council.org/ean_ucc_system/education_support/cdc.html |year=2006 |title=GS1 Check Digit Calculator |access-date=2008-05-21 |publisher=GS1 US |archive-url=https://web.archive.org/web/20080509141716/http://www.uc-council.org/ean_ucc_system/education_support/cdc.html |archive-date=2008-05-09 }}</ref><ref>{{cite web |url=https://www.gs1.org/services/how-calculate-check-digit-manually |title=How to calculate a check digit manually |date=5 November 2024 |publisher=GS1}}</ref>

# Add the digits in the odd-numbered positions from the left (first, third, fifth, etc.—not including the check digit) together and multiply by three.
# Add the digits (up to but not including the check digit) in the even-numbered positions (second, fourth, sixth, etc.) to the result.
# Take the remainder of the result divided by 10 (i.e. the modulo 10 operation). If the remainder is equal to 0 then use 0 as the check digit, and if not 0 subtract the remainder from 10 to derive the check digit.

A GS1 check digit calculator and detailed documentation is online at GS1's website.<ref name=GS1>{{cite web |url=http://www.gs1.org/barcodes/support/check_digit_calculator |year=2005 | title=Check Digit Calculator |access-date=2008-05-21 |publisher=GS1}}</ref> Another official calculator page shows that the mechanism for GTIN-13 is the same for [[Global Location Number]]/GLN.<ref name=GS1calculator>{{cite web |url=http://www.gs1us.org/resources/tools/check-digit-calculator |title=Check Digit Calculator, at GS1 US official site |access-date=2012-08-09 |publisher=GS1 US |archive-date=2016-11-21 |archive-url=https://web.archive.org/web/20161121055649/http://www.gs1us.org/resources/tools/check-digit-calculator |url-status=dead }}</ref>

For instance, the UPC-A barcode for a box of tissues is "036000241457". The last digit is the check digit "7", and if the other numbers are correct then the check digit calculation must produce 7.
# Add the odd number digits: 0+6+0+2+1+5 = 14.
# Multiply the result by 3: 14 × 3 = 42.
# Add the even number digits: 3+0+0+4+4 = 11.
# Add the two results together: 42 + 11 = 53.
# To calculate the check digit, take the remainder of (53 / 10), which is also known as (53 modulo 10), and if not 0, subtract from 10. Therefore, the check digit value is 7. i.e. (53 / 10) = 5 remainder 3; 10 - 3 = 7.
Another example: to calculate the check digit for the following food item "01010101010'''''x'''''".
# Add the odd number digits: 0+0+0+0+0+0 = 0.
# Multiply the result by 3: 0 x 3 = 0.
# Add the even number digits: 1+1+1+1+1=5.
# Add the two results together: 0 + 5 = 5.
# To calculate the check digit, take the remainder of (5 / 10), which is also known as (5 modulo 10), and if not 0, subtract from 10: i.e. (5 / 10) = 0 remainder 5; (10 - 5) = 5. Therefore, the check digit '''''x''''' value is 5.