Methodology & Data Sources

The calculator on the home page converts a historical football transfer fee into its equivalent in today's money. Instead of tracking general consumer prices, it tracks how much the transfer market itself has grown — because transfer fees have inflated far faster than the cost of living over the same period.

For each season from 00/01 to 25/26, the calculator holds an inflation coefficient — one for the combined top 5 European leagues (Premier League, Serie A, Bundesliga, LaLiga, Ligue 1), and one for each league individually. Coefficients are normalized so 00/01 equals a baseline of 1.0; a coefficient of, say, 3.4 means that season's transfer market moved roughly 3.4× the 00/01 baseline.

Converting a fee from one season to another applies a single ratio:

adjusted fee = fee × coefficient[target season] / coefficient[original season]

This is the same formula used everywhere fees are adjusted on this site, including the “Adjusted fee” columns on player and club transfer histories — always rebased onto the latest season (25/26, i.e. today's money).

The calculator's index covers 26 seasons (00/01 to 25/26) across the top 5 European leagues: Premier League, Serie A, Bundesliga, LaLiga, and Ligue 1.

The Players and Clubs sections cover a much wider scope — every league in the underlying dataset, not just the top 5 — since they draw on a separate, independently sourced database (see below) rather than the calculator's own season-by-season index.

Player profiles, club profiles, transfer records, and market valuations come from a database synced weekly from dcaribou/transfermarkt-datasets, an open-source project that aggregates public data from Transfermarkt. This site only reads that data — it doesn't scrape or republish Transfermarkt directly, and doesn't control how often or how completely any individual player or club record is updated upstream.

• Transfer and valuation dates are mapped to a football season assuming seasons run July–June; this is an approximation, not exact transfer-window data.
• Some players and clubs have sparse or incomplete records (no priced transfers, or fewer than two market-value data points) — those pages note this explicitly rather than showing an unexplained gap.
• "Current squad" figures reflect each player's most recent recorded season in the dataset, which may lag a live squad by the sync interval.
• The combined and per-league indices reflect aggregate market movement, not any single club's or player's actual purchasing power.

Spotted something that looks wrong, or have a question about how a figure was calculated? Open an issue on GitHub.