What is the Luhn algorithm?

The Luhn algorithm (also called Luhn formula or mod 10 algorithm) is a checksum formula used to validate credit card numbers, IMEI numbers, and other identification strings. It catches common data entry errors but is not a security measure — it's publicly known.

Does this validate if a card is active?

No. Luhn validation only checks the number structure and checksum. It cannot verify if a card is real, active, or has funds. For actual payment validation you need a payment processor like Stripe or Adyen.

Are the test card numbers safe to share?

Yes. The test numbers shown here are publicly documented test values (from Stripe and other payment processor docs). They pass Luhn but are not connected to real accounts. Never enter your actual card number in any online tool.

Credit Card Validator

Runs in browser

Luhn algorithm credit card validator. Detects 8 card types. Includes test numbers.

Validate credit card numbers using the Luhn algorithm. Detects Visa, Mastercard, Amex, Discover, JCB, Diners Club, UnionPay, and Maestro. Includes test card numbers. Browser-based — no data sent to server.

Card Number

✓ Valid

Visa · CVV: 3 digits

4242 4242 4242 4242

Luhn: ✓ Pass

Length: ✓ Valid

16 digits

Supported Card Types

Visa

Lengths: 13, 16, 19

Mastercard

Lengths: 16

American Express

Lengths: 15

Discover

Lengths: 16

JCB

Lengths: 16

Diners Club

Lengths: 14

UnionPay

Lengths: 16, 17, 18, 19

Maestro

Lengths: 12, 13, 14, 15, 16, 17, 18, 19

Test Card Numbers

Visa4242 4242 4242 4242

Mastercard5555 5555 5555 4444

Amex3782 8224 6310 005

Discover6011 1111 1111 1117

JCB3530 1113 3330 0000

Diners3056 9309 0259 04

These are publicly known test numbers that pass Luhn validation. Never use real card numbers.

🔒 Runs in your browser · No uploads · Your data never leaves your device

How to use

Enter a card number
Type or paste a card number. Spaces and dashes are allowed. The card type is detected automatically from the first digits.
Check the result
The tool runs Luhn validation and length check simultaneously. Both must pass for the number to be valid.
Use test numbers
Click 'Use' next to any test card number to load it. These are publicly known test numbers that pass Luhn — safe to share and test with.

Common use cases

Checking test card numbers for payment integration — Verify that Stripe, Braintree, or Adyen test card numbers pass Luhn validation before using them in your payment flow tests.
Validating user input before submitting to a payment API — Run Luhn validation client-side to catch obviously invalid card numbers before making an API call to a payment processor.

Examples

Visa test card
Load the Visa test number 4242424242424242
Output
```
✓ Valid · Visa · 16 digits · Luhn: Pass
```

Frequently asked questions

What is the Luhn algorithm?: The Luhn algorithm (also called Luhn formula or mod 10 algorithm) is a checksum formula used to validate credit card numbers, IMEI numbers, and other identification strings. It catches common data entry errors but is not a security measure — it's publicly known.
Does this validate if a card is active?: No. Luhn validation only checks the number structure and checksum. It cannot verify if a card is real, active, or has funds. For actual payment validation you need a payment processor like Stripe or Adyen.
Are the test card numbers safe to share?: Yes. The test numbers shown here are publicly documented test values (from Stripe and other payment processor docs). They pass Luhn but are not connected to real accounts. Never enter your actual card number in any online tool.

Key concepts

Luhn algorithm: A simple checksum formula used to validate identification numbers like credit cards and IMEI codes — catches common transcription errors.
IIN / BIN: Issuer Identification Number (first 6–8 digits of a card) used to identify the card network (Visa, Mastercard, etc.) and issuing bank.

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