Sanxenxo is overwhelmingly a summer destination. The town effectively runs from June to mid-September, with July and August the peak when prices double and Silgar beach disappears under towels. If you want the resort experience — busy promenade, every restaurant open, evening ambiente — those are the months to come.
June and early September are the better compromise: warm enough to swim, the sea around 19–20 °C, and a much more relaxed feel. The big traditional festivals — the August fiestas around the patron saints and the Bath of the Nine Waves at A Lanzada at the end of August — fall in this peak season.
Outside summer, the town is quiet. Many beachfront restaurants close from October to Easter. The compensation is mild weather, almost empty beaches, and Galician light at its best. The local Albariño harvest is in September and the wineries inland are welcoming during the vintage.