ISO 8601 Converter
Convert a date into every ISO 8601 form, including week and ordinal dates.
Luhn Validator
Check any number against the Luhn checksum and see the working.
Quick Tool Overview
The Luhn Validator checks a number against the mod-10 checksum and shows the working — which digits double, what each contributes, and the final total — because seeing it is what makes the algorithm implementable.
- What it does
- Validates a number against the Luhn checksum
- You give it
- Any number, with or without separators
- You get back
- A verdict plus the full calculation
- Best for
- Card numbers, IMEIs and any Luhn-checked reference
About the Luhn Validator
Paste a number and the Luhn checksum is calculated with the working shown: which digits are doubled, what each becomes, the running total and the final modulo. Seeing it is far more useful than a yes or no when you are implementing the check yourself.
The algorithm is used for far more than card numbers — IMEI numbers, some national identification numbers, and a variety of account references all use it. Where the input looks like a card number the scheme is identified from its prefix and length, and the expected check digit is shown when the number fails, which usually makes the typo obvious.
Key features of the Luhn Validator
The working shown
Each digit with whether it doubled and what it contributed, so you can implement the check yourself from what you see.
The expected digit
When a number fails, the check digit that would have been correct is given — which usually makes the typo obvious.
Scheme identified
A card number is matched to its scheme from the prefix and length.
Not just cards
IMEIs, some national identification numbers and many account references use the same checksum.
Clear about what it proves
Luhn catches typos. It says nothing about whether an account exists, and the page does not pretend otherwise.
How to use the Luhn Validator
-
1
Paste the number
Spaces and hyphens are ignored.
-
2
Read the verdict
Pass or fail, plus the check digit that would have been correct.
-
3
Follow the working
Each digit is shown with what it contributes to the total.
-
4
Check the scheme
Card numbers are identified from their prefix and length.
Frequently asked questions
Every single-digit error and almost every transposition of adjacent digits — which together are nearly all the mistakes a person makes typing a long number.
Swapping 09 for 90, which is the one transposition it misses. It also says nothing about whether the number corresponds to a real account.
IMEI numbers on phones, some national identification numbers, SIM card serials and a range of account references. It is a general-purpose checksum, not a payment-specific one.
Yes, as a courtesy — it catches a typo instantly instead of after a round trip. It is not a substitute for an authorisation, which is the only thing that proves a card is usable.
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