Credit Card Validator: Luhn Check & Card Type Detector

How to use this tool

Choose a synthetic test number. Select one of the sample buttons or enter a synthetic test number. Never enter a real payment card number.
Review the format checks. Read the detected network, Luhn checksum, and digit length. The number must pass both the checksum and the recognized network length to show Valid.
Use the check digit as a test aid. If the Luhn check fails, the tool shows the check digit calculated from the other digits. This is a format hint for synthetic test data, not payment authorization.

Credit Card Number Validator

Use a synthetic test number to check whether it passes the Luhn checksum, identify the card network (Visa, Mastercard, American Express, Discover, etc.), and verify that the length matches the expected format.

The Luhn Algorithm

The Luhn algorithm (also known as the "mod 10" algorithm) is a simple checksum formula used to validate identification numbers such as credit card numbers. It can detect any single-digit error and most transpositions of adjacent digits. It is not a cryptographic check: it only protects against accidental errors.

Privacy

All validation runs entirely in your browser using JavaScript. Your card number is never sent to any server. The test numbers shown are synthetic numbers for demonstration only.

Luhn algorithm: step-by-step walkthrough

Using the number 4539 1488 0343 6467 as an example:

Starting from the rightmost digit (the check digit), double every second digit going left.
If a doubled value exceeds 9, subtract 9 from it.
Sum all digits (original and doubled).
If the total is divisible by 10, the number is valid.

4 5 3 9 1 4 8 8 0 3 4 3 6 4 6 7  (original)
8 5 6 9 2 4 7 8 0 3 8 3 3 4 3 7  (doubled alternating, subtract 9 if > 9)
Sum = 8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80
80 mod 10 = 0 -> Valid

Card type IIN/BIN prefixes

Network	Starts with	Length
Visa	4	13, 16, or 19 digits
Mastercard	51–55 or 2221–2720	16 digits
American Express	34 or 37	15 digits
Discover	6011, 622126–622925, 644–649, or 65	16 or 19 digits
Diners Club	300–305, 36, or 38	14 digits
JCB	3528–3589	16–19 digits
UnionPay	62, except the Discover range above	16–19 digits
Maestro	6304, 6759, or 6761–6763	12–19 digits

These ranges are used only to estimate the network from the number's opening digits. The Discover 622126–622925 range overlaps the broader UnionPay 62 prefix, so this checker checks Discover first and treats other matching 62 prefixes as UnionPay. Issuer ranges may change, and a network match does not verify an account.

Test card numbers for developers

These synthetic numbers pass the Luhn check but are not real cards and cannot be charged:

Visa: 4242 4242 4242 4242 (Stripe test card)
Mastercard: 5555 5555 5555 4444
Amex: 3782 822463 10005
Discover: 6011 1111 1111 1117

Frequently asked questions

Does a valid result mean the card is active?

No. A valid result means only that the number passes the Luhn checksum and matches a recognized network prefix and length. This browser-only format check cannot confirm an account, available credit, or whether a payment would be authorized.

Should I enter a real card number?

No. Use synthetic test numbers such as the examples on this page. Never enter real payment card data into this tool or another third-party validator.

Which card networks can this tool recognize?

It checks common prefix patterns for Visa, Mastercard, American Express, Discover, Diners Club, JCB, UnionPay, and Maestro. Network ranges can overlap or change, so the detected name is a format hint rather than confirmation from an issuer.