AirHint found the following cheapest return flights from Trondheim (TRD) to Helsinki (HEL) in September 2025 (see full year).

Return flights

29 Sep - 03 Oct	Scandinavian Airlines
30 Sep - 04 Oct	Scandinavian Airlines
12 Sep - 15 Sep	Scandinavian Airlines
20 Sep - 22 Sep	Scandinavian Airlines
20 Sep - 22 Sep	Finnair	direct
30 Sep - 04 Oct	Finnair	direct
06 Sep - 08 Sep	Finnair	direct
28 Sep - 05 Oct	Scandinavian Airlines
28 Sep - 05 Oct	Finnair	direct

Also check the deals for one-way flights from Trondheim to Helsinki in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from Trondheim to Helsinki in September from 150€

Return flights