Saint-Tropez has the harbour photograph. No Marbella postcode reproduces the social density of Le Club 55, Sénéquier and the Place des Lices during the August fortnight when the global UHNW migrates south. What Saint-Tropez does not give the buyer — once the August crowd disperses — is a year-round home, school continuity or healthcare proximity. On annual wealth tax the two coasts are closer than either one's brochures admit: France charges the Impôt sur la Fortune Immobilière, and in Andalusia the state solidarity tax on large fortunes applies above its threshold.
This piece treats Saint-Tropez and the wider Var/Alpes-Maritimes trophy axis — Cap Ferrat, Cap d'Antibes, Ramatuelle, Pampelonne, Gassin — as the competing answer to a Marbella allocation in the €5M–€30M range. It does not pretend Marbella reproduces the Tropezian August. It does argue that the Tropezian August is sixteen weeks, and the other thirty-six weeks per year are where the real numbers live.
A €10M Saint-Tropez villa held by a French tax resident attracts roughly €100,000–€135,000 in annual IFI alone, plus taxe foncière €25,000–€50,000, plus the second-home taxe d'habitation surcharge of €10,000–€30,000 in coastal communes. The same €10M villa in Marbella's Sierra Blanca, held as net Spanish assets with no debt, is not free of wealth tax: €10,000,000 − €700,000 = €9,300,000, which on the solidarity-tax scale gives €39,915.97 + 2.1% × (€9,300,000 − €5,347,998.03) = about €122,900 a year (Article 3 of Ley 38/2022). To that add IBI — the cadastral value multiplied by the municipal rate, stated on the last receipt — and, for a non-resident who does not let, the tax on a deemed income. The annual difference between the two coasts depends on debt, ownership structure and residence; it is not a fixed sum in either coast's favour.
Inheritance is the second structural break. A €15M French villa transferred to two children attracts roughly €4.5M in droits de succession at top marginal rate. The same villa in Andalucía attracts under €100K thanks to the 99% bonificación.
Saint-Tropez wins on August social density, superyacht infrastructure and Belle Époque trophy patina at Cap Ferrat and Cap d'Antibes. Marbella wins on year-round usability, golf density and exit liquidity.
France publishes its completions through the Notaires de France statistics; Spain publishes none at property level. The Marbella side is therefore asking prices from our own register, and we will not present the two as one series.
The budget that buys a newly built designer villa on a large plot in Sierra Blanca — indoor and outdoor pools, gym, cinema, garage — buys a smaller renovated villa on a tight plot on Cap Ferrat, often without sea frontage. Current asking prices by zone, each with its sample size and date, are on the Marbella Property Index (museselection.es/marbella-property-index).
The trophy band tightens further. At the very top, the Riviera offers a Belle Époque Cap Ferrat villa with provenance or a Cap d'Antibes trophy with private beach access; Marbella offers a La Zagaleta gated estate on a far larger plot. Per metre the Riviera asks a multiple of Marbella for comparable formats; no public dataset measures that multiple, because Spain publishes no per-property closing prices.