The peak season on Milos runs from late June through September, with July and August being the busiest and most expensive months. During this period everything is open, boat tours run daily to Kleftiko and the sea caves, and the beaches are lively. The downside is that accommodation prices are high, the best spots fill up early in the day, and the meltemi — the strong seasonal north wind that sweeps the Aegean in midsummer — can make the northern beaches choppy and occasionally shut down access to sea caves like Kleftiko entirely.
May and October are the ideal months for most visitors. The weather is warm enough to swim, the island is noticeably quieter, prices drop sharply, and you will have Sarakiniko largely to yourself at sunrise. The landscape in May is also greener than the parched summer palette. November through March is a different island altogether: many hotels, restaurants, and boat operators close for the winter, and the population retreats to its core. The island is peaceful and genuine in winter, but you need to plan around limited services. Easter weekend brings a brief burst of Greek domestic tourism and is well worth experiencing if your dates allow.