The timing of Eid is traditionally dependent on when the new moon becomes visible, and local imams are usually depended upon to provide guidance. Eid marks the end of the Ramadan month of fasting.
It was unclear until late on Thursday whether Eid would start on Friday or Saturday, but after meetings, moon observations and talks with Muslim bodies in other European countries, it was decided to start the festival on Friday.
"The most important thing is that we can unite as many Swedish Muslims as possible around the same day," said Abdallah Salah, chairman of the Islamic Association in Stockholm.
Around 400,000 people with Muslim backgrounds in Sweden are expected to celebrate Eid, a festival which can be compared in some ways to Christmas in the Christian world. The festival lasts three days, and families give presents to children.