# Check Digit Calculator (GTIN, UPC, EAN, SSCC)

URL: https://speedycalculator.com/calculators/finance/gtin-check-digit/
Last updated: 2026-10-25

> The check digit calculator works out the GS1 check digit for barcodes – GTIN-8, UPC-A (GTIN-12), EAN-13 / ISBN-13, GTIN-14 and SSCC-18 – using the standard mod-10 algorithm, and shows the full code.

## Inputs

- Barcode digits (without the check digit)
- Leading zeros to add

## Results

- Check digit
- Complete code
- Code type

## Formula

```
From the right (excluding the check digit), multiply digits alternately by 3 and 1
Sum the products
Check digit = (10 − sum mod 10) mod 10
```

## Explanation

The check digit lets scanners detect most typing and scanning errors. GS1 issues company prefixes; you can't make up valid retail barcodes, but you can verify or complete one. Everything is calculated in your browser, so nothing you type is sent to our server.

### How to use the Check Digit Calculator

- **Barcode digits (without the check digit)**
- **Leading zeros to add**

Everything runs in your browser, so results appear instantly and nothing you type is sent to a server.

### How it works

Type the barcode digits without the check digit; add leading zeros to convert between formats (e.g. UPC to GTIN-14).

### Tips

- Know the difference between margin (profit ÷ price) and markup (profit ÷ cost).
- Apply successive discounts one after another – they do not simply add up.
- Check whether prices already include sales tax or VAT.
- Round prices only at the very end of the calculation.

### Common mistakes to avoid

- Adding discount percentages together.
- Pricing from a target margin using the markup formula.
- Forgetting payment-processing and shipping fees.

## Worked example

Inputs — Barcode digits (without the check digit): 62910415002; Leading zeros to add: 0.

Results — **Check digit = 4**; Complete code = 629104150024; Code type = GTIN-12 (UPC-A).

## FAQ

**What is a check digit?**
The last digit of a barcode, calculated from the others to catch errors.

**How is a UPC check digit calculated?**
Weights 3 and 1 alternate from the right; the check digit brings the sum to a multiple of 10.

**Is the ISBN-13 check digit the same?**
Yes – ISBN-13 uses the EAN-13 algorithm.

**What formula does the Check Digit Calculator use?**
From the right (excluding the check digit), multiply digits alternately by 3 and 1.


## Sources

- [GS1 – Check digit calculator](https://www.gs1.org/services/check-digit-calculator)