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, healthcare proximity, or a tax framework that survives a 10-year hold without bleeding €150,000–€250,000/year to the French Impôt sur la Fortune Immobilière. For most HNW buyers running an honest after-tax IRR comparison in 2026, Marbella wins by a margin that is wider than the brochures admit.
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 attracts zero Andalucían wealth tax, IBI €8,000–€15,000, and IRNR €8,000–€10,000 if non-resident. Annual cash outflow delta: €120,000–€180,000 in Marbella's favour, every year.
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 after-tax cost, year-round usability, golf density and exit liquidity.
Figures combine Notaires de France quarterly statistics for Var and Alpes-Maritimes, Sotheby's International Realty French Riviera reports, Tinsa-verified Marbella completions, and Knight Frank Wealth Report 2024 cross-referencing.
A €15M Sierra Blanca purchase buys a 1,200–2,000 m² newly built designer villa on a 3,500–7,000 m² plot with indoor and outdoor pools, smart-home, gym, cinema and garage for four cars. The same €15M on Cap Ferrat secures a 350–500 m² renovated villa on a tight plot, often without sea-frontage. On Cap d'Antibes you might secure 600–800 m² but the trophy stretches above La Garoupe begin at €25M.
The trophy band tightens further. €30M+ secures a Belle Époque Cap Ferrat villa with provenance or a top Cap d'Antibes trophy with private beach access. The same €30M in Marbella secures a top La Zagaleta gated estate at 4,000+ m² of build on 10,000+ m² of plot with helipad. Per-metre, the Riviera trophy band runs 4x–6x Marbella for comparable formats; per-plot the gap is wider still.