However the city is at its best during summer months (May to September) when the weather is mild and also the majority of travellers flock in during that time. But keep in mind the summer holidays in Finland commence from July which translates to higher prices, some business to be closed and also obtaining of prior reservations. Also the annual rainfall picks up from August-September. So all in all, the best time to visit, since Helsinki is pleasant all throughout the year, is June. If you’re on a budget, the best time to visit is September and October with very little crowd. But on the downside, many attractions will be closed during that time.