### Check Digit A decimal (or alphanumeric) digit added to a number for the purpose of detecting the sorts of errors humans typically make on data entry.

### Check Equation

An equation which all the digits in a number, including the check digit, must satisfy.
We can eliminate (or easily detect) the problem of omitting or adding digits by restricting the input field to a given number of digits if we are dealing with numbers which are fixed in format, such as credit card numbers, Social Insurance Numbers, local phone numbers, and student ID numbers.

Other errors are detected by calculating whether the check equation for a particular check digit scheme is true. The check digit is included in the equation so that it is protected against errors as well. If the equation is not true, an error is present; if it is true, there may or may not be an error.

### Check Digit Calculator

The last digit of a bar code number is a computer Check Digit which makes sure the bar code is correctly composed.

Click on the following box to calculate the check digit direclty:

### How to Calculate a Check Digit Manually?

The following table  explain how to calculate the Check Digit manually for GTINs:

 ID Key Format Digit positions GTIN-8 N1 N2 N3 N4 N5 N6 N7 N8 GTIN-12 N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 GTIN-13 N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 GTIN-14 N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 N14 SSCC N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 N14 N15 N16 N17 N18 Step 1: Multiply value of each position by x3 x1 x3 x1 x3 x1 x3 x1 x3 x1 x3 x1 x3 x1 x3 x1 x3 Step 2: Add results together to create sum Step 3: Subtract the sum from nearest equal or higher multiple of ten = Check Digit

The following table gives an example to illustrate how a Check Digit is calculated:

 Positions N1 N2 N3 N4 N5 N6 N7 N8 N9 N10 N11 N12 N13 Number without Check Digit 6 2 9 1 0 4 1 5 0 0 2 1 - Step 1: Multiply x x x x x x x x x x x x - by 1 3 1 3 1 3 1 3 1 3 1 3 - Step 2: Add results = = = = = = = = = = = = - to create sum 6 6 9 3 0 12 1 15 0 0 2 3 = 57 Step 3: Subtract the sum from nearest equal or higher multiple of ten = 60- 57 = 3 (Check Digit) Number with Check Digit 6 2 9 1 0 4 1 5 0 0 2 1 3