Compute the Luhn check digit for a number.
Please do not make financial decisions based on these results.
What is the Check Digit Calculator?
Compute the Luhn check digit for a number. To use the Check Digit Calculator, enter number without check digit; it returns check digit, and shows them instantly as you type.
Where the Check Digit Calculator fits
Compute the Luhn check digit for a number. The main figure it returns is the Check digit, worked out from the values you enter.
It belongs with the other sales, discounts & pricing tools. If you are comparing options or checking a result from another angle, try the Cyber Monday Calculator, Margin and Markup Calculator or the Margin and Sales Tax Calculator.
How to use the Check Digit Calculator
- Enter your numbers. The inputs are Number without check digit. Use real figures from your own records where you can. Fields marked optional can stay at zero.
- Read the result. The highlighted box gives the Check digit. Tables and charts break it down further.
- Test other scenarios. Results update as you type. Change one value at a time to see what drives the answer, and press Reset to go back to the defaults.
Formula and how it works
Example with real numbers
Here is the Check Digit Calculator using the default values shown in the calculator above:
Inputs
| Number without check digit | 7992739871 |
|---|
Results
| Check digit | 3 |
|---|
With these inputs the calculator returns Check digit: 3. Change any value in the calculator to see how the result moves.
Method and limits. This calculator applies the formula in the section above to your inputs, in your browser; nothing you enter is stored on our servers. The result is only as accurate as the numbers you enter and the formula shown above. It is for information, not financial, tax or legal advice.
Frequently asked questions
What is the Luhn algorithm?
A checksum used on credit card and ID numbers to catch typing errors.
What is the difference between margin and markup?
Margin is profit as a share of the selling price; markup is profit as a share of cost. A 50% markup equals a 33% margin.
Is sales tax included?
Only where a tool has a tax field. Enter your own local rate because it varies by location.
Are the results guaranteed?
No. Results depend entirely on the numbers you enter and the formulas shown on this page. Please do not make financial decisions based on them alone; confirm important figures with a licensed professional.
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