You've been sent an invoice from a supplier in Germany, or a landlord in Spain, or a freelancer in France, and at the bottom there's a long string of letters and numbers labelled "IBAN". Your banking app wants you to type it in, and maybe a SWIFT/BIC code too. One wrong character and the payment can bounce, get delayed for days, or in the worst case land somewhere it shouldn't.
The good news: an IBAN is designed to be checkable. You can catch most typing mistakes before you press "send". This guide walks through what an IBAN actually is, how the built-in check works, and a simple routine for checking the details before any international transfer.
What an IBAN is (and what it isn't)
IBAN stands for International Bank Account Number. It's defined by the ISO 13616 standard and is used across Europe and in a number of countries in the Middle East and elsewhere. Every IBAN follows the same basic shape:
- Country code – two letters, such as DE for Germany or FR for France.
- Check digits – two numbers that let software verify the rest of the IBAN.
- BBAN – the Basic Bank Account Number, a country-specific block that contains the bank identifier and the account number.
The total length is fixed per country. A German IBAN is always 22 characters, a French one is 27, a Belgian one is 16. If the IBAN you've been given is the wrong length for its country, something has definitely gone wrong.
What an IBAN is not is a guarantee that the account belongs to the person you think it does. It identifies an account; it doesn't prove ownership. Keep that in mind, because it shapes what a checker can and can't do for you.
How the MOD 97 check catches typos
Those two check digits are the clever part. The standard uses a calculation called MOD 97: the first four characters are moved to the end, letters are converted to numbers, and the resulting very long number is divided by 97. For a valid IBAN, the remainder must be exactly 1.
Why does this matter to you? Because almost every common typing mistake breaks that calculation. Swap two neighbouring digits, drop a character, or mistype a single number, and the remainder will almost certainly no longer be 1. That's how a validator can tell you "this IBAN is invalid" without contacting any bank at all.
You don't need to do the arithmetic by hand. A tool like the free IBAN validator on IBANtool checks the format, the length for the country, and the MOD 97 check digits in one go, and breaks the IBAN into its country, check-digit, and BBAN parts so you can see exactly what you're looking at. According to the site, validation runs in your browser and the IBAN you type isn't uploaded to its server, which is a sensible design for something as sensitive as account details.
A 5-step routine before every international transfer
1. Copy, don't retype
Whenever possible, copy the IBAN directly from the invoice PDF or email rather than typing it from a screenshot. Most errors are introduced by retyping. If you must type it, do it in groups of four characters, the way IBANs are usually printed.
2. Check the country code and length
Look at the first two letters. Does the country match where your recipient's bank actually is? Then check the length. If you're paying a German account, it should be 22 characters. IBANtool has a page for each supported country, for example the German IBAN format and example, showing the expected length and structure, which is handy when you're dealing with a country you haven't paid before.
3. Run it through a validator
Paste the IBAN into a validator. If it fails, don't try to "fix" it yourself by guessing which digit is wrong. Go back to the recipient and ask them to resend their details. If it passes, you've ruled out the most common category of error: simple typos.
4. Get the right SWIFT/BIC code
Many cross-border transfers also ask for a SWIFT or BIC code, an 8- or 11-character identifier for the receiving bank. The first four characters identify the bank, the next two the country, the next two the location, and an optional three-character suffix can point to a specific branch.
Because one bank brand can have different BICs in different countries, a code that "looks right" can still be wrong. If you already have the IBAN, the IBAN to SWIFT tool extracts the country and bank code from it and suggests a matching BIC where the site's directory has an exact mapping. Treat that as a cross-check: if the recipient's own payment instructions give a different BIC, their instructions should win, and it's worth asking them to confirm.
5. Confirm the name and the details through a second channel
This is the step people skip, and it's the one that protects you from fraud. Invoice-redirection scams work by sending you a perfectly valid IBAN, just not the one belonging to your real supplier. A validator will happily say "valid" because, mathematically, it is.
If the payment is large, or if you receive an email saying "our bank details have changed", confirm the details by phone or through a contact method you already trust, not by replying to the same email. Some banks also offer a payee-name check when you set up a new recipient; use it if yours does.
Common mistakes to watch for
- Letter O vs number 0, letter I vs number 1. These are the classic culprits. The check digits will usually catch them, which is exactly why running a validator is worth the ten seconds.
- Extra spaces or invisible characters. Copying from PDFs sometimes adds odd characters. Good validators strip spaces, but if something looks off, retype the spaces manually.
- Using a domestic account number instead of an IBAN. Not every country uses IBANs. The US, for example, doesn't; transfers there typically rely on account numbers plus routing details. If your recipient is outside the IBAN system, ask what their bank needs.
- An outdated SWIFT code. Banks merge and restructure. Always prefer the code on the recipient's current payment instructions over an old saved payee.
A note for developers and testers
If you build checkout pages, invoicing tools, or payroll forms, you'll need realistic IBANs to test with, and you should never use real customer accounts for that. IBANtool also offers an IBAN generator that creates random, MOD 97-valid test IBANs by country, which is useful for making sure your form accepts valid input and rejects the rest.
The bottom line
Checking an IBAN takes less than a minute and removes the most common reason international payments fail: a simple typo. Validate the IBAN, cross-check the SWIFT/BIC code, and for anything important, confirm the details with the recipient through a channel you trust. That combination catches both honest mistakes and the dishonest ones.
If you also work with audio or video for your business, you might find another tool we like useful: GetVocalRemover for separating vocals from music tracks.
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