Helsinki is 0.5 hours behind Tehran
Best overlap: 8:30 AM to 6:30 PM in Tehran is 8:00 AM to 6:00 PM in Helsinki.
For the smoothest call, aim inside 8:30 AM to 6:30 PM in Tehran, i.e. 8:00 AM to 6:00 PM in Helsinki. This is one of the easier pairings: 10 hours of shared time means flexible, low-stress scheduling. For part of the year the maths changes: Helsinki observes daylight saving, Tehran does not, shifting the overlap by an hour.