September is the month Greece specialists keep recommending, and for good reason. The Aegean has warmed all summer, ferries still run frequent services on the main routes, and the Cyclades' most in-demand hotels stay busy without the crush of August. Late May to early June is the other golden window: wildflowers are out, the weather is comfortable, though the sea can still feel brisk.
For sightseeing rather than swimming, aim for April or May, when cooler temperatures make exposed sites like the Acropolis and the open-air theatre at Epidaurus far more pleasant. In high summer, book the earliest possible entry slot at archaeological sites — extreme heat in recent years has forced abrupt closures, and Greece's Civil Protection agency publishes a daily wildfire risk map worth checking before any rural drive.
If price is the priority, November through March is the budget window, excluding Christmas and New Year. International flights can drop 30 to 50 percent below high-season fares, and Athens and Thessaloniki keep their museums and neighbourhood tavernas running all winter. On the islands it's a different story: many resorts shut from roughly November to April, so always cross-check hotel closing dates and ferry timetables before committing to a late-season stay.
One date that catches travellers out is Orthodox Easter, which often falls on a different weekend than the Western holiday. It fills rooms fast in places famous for their Holy Week traditions. Corfu's brass bands lead Good Friday processions and residents hurl clay pots from balconies on Holy Saturday morning; on Patmos, the abbot of the Monastery of St. John washes the feet of twelve monks in Chora's square; and in Leonidio in the Peloponnese, paper balloons rise over the town at midnight. Arrive before the weekend if you want any of it.
July and August remain peak — crowded, expensive, and busy right through mid-September now, especially around August 15, when Greece itself goes on holiday for the Feast of the Dormition and village panigiria feasts run long into the night. Ferries fill up, so book as soon as schedules open.
For a first trip, aim for about seven nights: two or three days in Athens, a couple on an island such as Santorini or Mykonos, and perhaps a mainland day trip to Delphi or Meteora. Allow at least three nights on any island — transfers eat up more time than you'd expect. If you'd rather skip ferry-hopping entirely, Crete can fill a whole week; base yourself in Heraklion for Knossos or Chania for the western beaches and White Mountains.
Beyond the beach, the Peloponnese rewards a spring or autumn road trip from Nafplio, and the mountain villages of Zagori in the northwest are made for walking. Snow has become less dependable for skiing at Arachova or Mainalo, so check lift conditions close to departure.