There will probably be a Frozen 4, by the way
Before we even have a release date for Frozen 3, Disney CEO Bob Iger has announced a Frozen 4

If there’s one rule of the modern movie business, it’s “milk a good thing for all it’s worth.” Disney’s animated divisions have traditionally been fertile ground for new and innovative storytelling, but they’re now heavily in the business of sequels. Earlier this year, the company’s CEO Bob Iger announced a new Toy Story, a new Zootopia, and a new Frozen. And, oh, by the way, now there’s already another new Frozen.
“Frozen 3 is in the works, and there might be a Frozen 4 in the works too,” Iger teased Thursday during an appearance on Good Morning America. “But I don’t have much to say about those films right now. [Director] Jenn Lee, who created the original Frozen and Frozen 2, is hard at work with her team at Disney animation on not one but actually two stories.”