The Oslo City Court's Web site gives Aug. 24 as the deadline, Views and News from Norway reported. The court originally promised a decision by July 20, two days before the first anniversary of his killings.
The verdict is to be broadcast live in Norway.
On July 22, 2011, Breivik planted bombs in two government buildings in Oslo, killing eight people. Posing as a police officer, he then shot scores more at a Labor Party summer camp on Utoya Island, killing 69 people, mostly teenagers.
An administrative court judge told the Norwegian Broadcasting Corp. the court needs some flexibility.
"We can't release it until everything is in place," Ina Stromstad said. "We're planning for July 20, but must have an alternative date as well."
Breivik contends he is sane. Defense witnesses have been testifying about the source of his extreme right-wing views.
Mattias Gardell, an expert on comparative religion from Sweden's Uppsala University, testified Monday that Breivik is "a product of a political milieu with a long tradition that he wanted to inspire."