Each marketplace shows a VAT-inclusive price. We strip each store's domestic VAT to a net base price: b = price / (1 + vat). Because intra-EU B2C is taxed at destination (the OSS regime), a buyer's home VAT applies uniformly to whichever store they buy from — so it cancels in every ratio. What remains is pure base-price divergence, not fiscal arbitrage.
Per product, the coefficient of variation of net prices across the euro-zone core. The category PFI is the median of those CVs; the headline PFI is category-balanced. A product must be in stock in at least two euro-zone stores to count.
For each country, the average premium a shopper pays versus the cheapest euro-zone market for the same product — the money left on the table by the single market.
Euro-zone core: Germany, France, Italy, Spain, Netherlands, Belgium. Poland and Sweden are FX-converted (ECB daily rate) and shown separately. The UK is excluded from single-market figures (post-Brexit customs/VAT).
Prices come from Amazon's EU marketplaces. This measures dispersion on Amazon, not all retail — Amazon's share varies by country. Same-ASIN items can differ by pack or edition; implausible spreads are quarantined, never headlined. Low-coverage categories (n<8) show uncertainty and are never put in a headline. Every figure is dated and shows its sample size. We never publish a number we can't defend.