An IBAN transfer is not a rail, it is an address format, and that distinction explains why answers to this question vary so wildly. Two payments quoted with an IBAN can travel by completely different routes: one inside a single shared clearing area that guarantees a deadline, the other through a chain of correspondent banks that guarantees nothing. What the IBAN is doing is the same in both cases.
Inside the euro area
Where both accounts are in the single euro payments area and the payment is in euro, it travels on a shared scheme with a defined deadline: a credit transfer must reach the beneficiary bank by the end of the next business day, and the instant variant settles in seconds where both banks support it. This is the case people have in mind when they say an IBAN transfer is fast, and within that area it genuinely is.
Outside it, with an IBAN
Many countries outside the euro area also issue IBANs, the United Kingdom among them. A payment quoted with a UK IBAN from outside Europe is an ordinary cross border transfer that happens to use a tidy address format. It goes through correspondent banks, inherits their cut-offs and screening, and takes what such a payment takes, commonly a day to several. The IBAN removes ambiguity about the account; it does not shorten the chain.
What the IBAN actually buys you
Fewer repairs. The check digits mean a malformed IBAN is rejected at the point of entry rather than travelling and failing at the far end, and the fixed structure means the receiving bank can identify the account mechanically. Payments that fail on details are a large part of the tail in international transfer times, so removing that failure mode shortens the average even where it does nothing to the best case.
What still goes wrong
A correct IBAN with the wrong beneficiary name still goes to repair at the far end, because there is no name check before sending on most cross border corridors. A currency the receiving account cannot hold causes a conversion or a return. And an IBAN for a closed account is a valid string pointing at nothing, which will be returned after it has travelled. None of these is an IBAN problem, but all of them show up in the answer to how long the transfer took.
Questions people ask about how long does an iban transfer take
Is an IBAN transfer faster than a normal transfer?
Inside the euro area, yes, because it travels on a shared scheme with a deadline. Outside it, an IBAN is an address format and the journey is an ordinary cross border one.
Does the United Kingdom use IBANs?
Yes for payments crossing a border. A UK IBAN contains the sort code and account number, and domestic payments use those directly instead.
Why did my IBAN transfer take a week?
Usually a correspondent chain, a missed cut-off, or a repair at the far end where the beneficiary name did not match. Ask your bank to trace it.
Can an IBAN transfer be instant?
Within the euro area, yes, where both banks support the instant scheme. Across other borders there is no instant equivalent.