Check Digit Validator

What it's for

Most account, product and ID numbers end in a check digit worked out from the others, so that a mistyped digit or two digits swapped are caught before the number is used. This checks it for the common kinds, tells you what the number is, and if the check fails, what the check digit should have been.

For example, when a supplier’s IBAN is rejected by your bank’s form, paste it here to see whether it was copied wrongly (and whether it’s even the right length for its country) before you ask them again.

How to use it

Type or paste the number. Spaces, hyphens and dots are ignored, as are a leading ISBN, ISSN or an https://orcid.org/ address. It’s checked as you type against every kind whose shape it fits:

• IBAN (international bank account number): the length for its country and the mod-97 check.
• ISIN (a share or bond’s ID), VIN (a vehicle’s), ORCID iD (a researcher’s).
• ISBN-13, ISBN-10 and ISSN for books and journals.
• GTIN barcodes: EAN-8, UPC-A, EAN-13 and GTIN-14.
• NHS number and ABA routing number (US banks).
• Luhn, used by payment cards (the brand is named from the first digits), phone IMEIs, Canadian SINs and many others.

When the number passes as one or more kinds, only those are listed. When it passes as none, every kind it could be is listed, each with the check digit it would need.

Type ? for a character you don’t know (up to two), and every value that makes the check work is listed: a way to fill in a smudged digit, or to make the check digit for a new number. Copy a link to this input keeps the number, so don’t use it for a real card number.

Example

Choose Try an example, which types this:

GB82 WEST 1234 5698 7654 32

It’s a valid United Kingdom IBAN of 22 characters. Change the 82 to 81 and it fails, with the note that the check digits would be 82. Then try 978-0-306-40615-? to see the last digit of that ISBN worked out as 7.

Good to know

A check digit only shows the number is well formed, not that it exists: a valid IBAN may still be a closed account, and a valid card number may never have been issued. Luhn misses a few swaps (09 and 90), and a number that is short enough can pass as more than one kind by chance (an ISBN-10 and an NHS number are worked out the same way). UK sort codes and account numbers are checked by a table the banks keep to themselves, so they aren’t here. Nothing you type leaves the page.