The best time to visit Schongau is from May to October, when the weather is warm enough to walk the town walls and cycle the Lech valley comfortably. Summer (July and August) brings the most reliable sunshine and the highest visitor numbers on the Romantic Road, though Schongau itself stays much quieter than its famous neighbours. The Alps are visible to the south on clear days, which tend to come most reliably in early summer and early autumn before the haze builds.
September and October are particularly good: the light is sharp, the crowds are thinner, and the Lech valley has autumn colour. The Wittelsbacher Tor and the southern wall section look especially good in low golden light.
Winter is quiet and cold, with limited opening hours at the Stadtmuseum, but the town has an atmospheric small Christmas market in December. Snow can fall from November to February and makes the old town photogenic, if chilly. Spring (April and May) is pleasant once the weather settles, with blooming meadows in the Lech valley.