How do add-ons work in football transfers?

- Published
It is common practice these days for transfer fees to have performance-based add-ons. The theory is the selling club gains more if the player goes on to be extremely successful, while the buying club is to some extent protected financially if the transfer doesn't work out.
In some cases, the total value of add-ons is significant - Real Madrid could end up paying an extra £30m to Borussia Dortmund for Jude Bellingham depending on how successful he is over the course of his career in the Spanish capital, for example.
In others, like the potential £1.7m worth of add-ons Brighton's £29.78m signing of Greece Under-21 forward Charalampos Kostoulas, are less significant.
Clubs sometimes say add-ons are 'easily achievable' or 'difficult'.
Easier-to-achieve add-ons can include things like making a basic number of appearances, or scoring a certain amount of goals. Add-ons can also be attached to a team's success rather than the individual player's - a club may agree to an add-on requiring an extra payment if they qualify for Europe, for example.
Others can be more ambitious - tied to extreme levels of individual or collective success, like winning the Champions League or the Ballon d'Or.
An example of the difficulty add-ons can present when discussing valuations would be the claims made in the Portuguese media in 2022 that the first additional payment in Darwin Nunez's £64m-plus-add-ons move from Benfica to Liverpool was triggered by the Uruguayan making just 10 appearances.
Then Liverpool boss Arne Slot rejected speculation he had not started Nunez in some games because it would trigger an additional payment.
Whether Liverpool paid more for Nunez, or club captain Virgil van Dijk - for whom they paid a flat fee of £75m to Southampton in 2017 - cannot be determined without knowing exactly what add-ons were included in the Nunez deal, then figuring out which conditions he has and has not met.