Despite the monster debut of Disney’s “Frozen 2” on Thursday, box office sales are slipping this year — and could fall further next year.

Weighed down by a trio of flops — Stephen King’s “Doctor Sleep,” “Terminator” sequel “Dark Fate,” and the remake of “Charlie’s Angels” starring Kristen Stewart — the box office is headed for a 4% sales dip, according to Eric Wold, analyst with financial research firm B. Riley FBR.

The slump comes even as Disney’s “Frozen 2” is projected to bring in more than $100 million in North American ticket sales this weekend, following an impressive $8.5 million opening night on Thursday. “The Joker,” starring Joaquin Phoenix, has also done well, pulling in $96.2 million in its opening weekend.

But neither Queen Elsa, the lead character in “Frozen 2,” nor Batman’s rival “The Joker” will be able to save movie theaters like AMC, Cinemark, Imax and Marcus Corp. from falling short of 2018’s highest-grossing year ever at the domestic box office with ticket sales falling just shy of $11.9 billion, Wold said.

Opening weekend numbers for “Doctor Sleep” hit $14.1 million as “Terminator” grabbed $29 million and “Charlie’s Angels” amassed a paltry $8.4 million, according to movie sales website Box Office Mojo.

“If a movie frankly stinks, people won’t go,” Wold told The Post. “Social media tells you if a movie wasn’t that good. Word gets out quickly. Movies have to open really strong or people will say: ‘I’ll skip it.’”

According to Wold, even the planned December release of several highly anticipated blockbusters — like “Jumanji: The Next Level” and “Star Wars: The Rise of Skywalker” — won’t be enough to eke out a flat 2019.

And next year’s slate won’t bolster the box office’s fate because “Avatar 2” will hit theaters in 2021, not 2020, due to scheduling shifts from its distributor, Disney, Wold said.

The last time the box office suffered two consecutive years of souring sales was 2010 and 2011, when ticket sales totaled $10.5 billion and $10 billion, respectively.

The crunch for movie theaters comes as consumers have more places, like Netflix and Disney+, to watch TV and movies. Next year, a host of new streaming services, such as HBO Max, Quibi and NBCUniversal’s Peacock, will enter the market.

“It’s tough these days, people have so many other options, it’s not just streaming,” Wold said.

In good news, the analyst predicted that “2021 will be a phenomenal year,” bolstered by a handful of big budget movies like “The Batman,” “Mission Impossible 7,” “Cinderella,” “Jurassic World 3” and a “Spider-Man” sequel.