Donauwörth is a year-round town without strong seasonal peaks. Summer brings the best weather for walking the Reichsstraße and sitting by the Danube, and the late-July Schwäbischwerder Kindertag pageant — in which hundreds of local children dress in historical costume and re-enact scenes from the town's past — is one of the more charming local festivals on the Romantic Road. It has been running for well over a century and draws a genuinely local crowd rather than a tourist one.
Spring and autumn are quieter and often more pleasant for visiting the churches and museum: the light is good, the Romantic Road coach tours are thinner on the ground, and accommodation is easier to come by. Winter is cold and can be grey, but the Christmas market on the Reichsstraße is modest in scale and not yet overwhelmed by visitors the way larger Bavarian markets have become.
Avoid the town in late February if you are sensitive to the anniversaries of difficult history: the bombing raids of February 25, 1945 that destroyed much of Donauwörth are still remembered locally.