50 most expensive transfers of summer window, ranked by true cost: Isak isn't No. 1

"But €50 million in 2025 is a lot different from €100 million in 2015, and money spent by PSG is a lot different from money spent by, say, Marseille or Mallorca. In an era where nearly every league and UEFA have spending rules pegged to a certain percentage of team revenue, perhaps there's a better way to compare transfer spending -- across teams and across eras."

"If we look at Neymar's transfer as a percentage of PSG's revenue for the 2017-18 season, then it accounts for 40% of it. That seems like a lot -- and it is. Clubs tend to pay somewhere between 15% and 20% of their revenue for their most expensive signings. Neymar, of course, was double that. But that's not as much as Real Madrid paid for Zinedine Zidane in 2001."

"Kicking the Galacticos era into full swing, Madrid broke the transfer fee record to acquire a 29-year-old (!) Zidane for €77.5 million -- or 51% of their revenue. And that's not as much as Real Betis paid to acquire Denilson three years prior. Their €30 million move for the 20-year-old Brazilian was at least 60% of their revenue. I say "at least 60%" because I don't have access to their revenues in 1998."

Absolute transfer fees can mislead because inflation, market growth and club wealth vary across years and teams. Evaluating transfer fees as a percentage of club revenue provides a clearer measure of spending impact across clubs and eras. Neymar's €222 million move represented about 40% of Paris Saint-Germain's 2017–18 revenue, while clubs typically allocate 15–20% of revenue for their costliest signings. Real Madrid's €77.5 million signing of Zinedine Zidane equaled roughly 51% of Madrid's revenue in 2001. Real Betis' €30 million purchase of Denilson in 1998 amounted to at least 60% of Betis' revenue, showing larger relative burdens in earlier periods.

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