The bottom line growth would be a huge achievement for the home and apartment sharing company that just a few years ago was among a number of so-called Unicorns that seemed to have a lot of potential, but not much in the way of profits. It would also make Airbnb the first company to prove that the so-called sharing economy can be turned into sustainable success. That’s something that Uber, the sector’s other superstar, has yet to prove.

The numbers are according to a source familiar with the company’s internal estimates, and haven’t previously been made public, though Bloomberg previously reported the company turned its first profit in 2016.

Despite the projected bottom line growth, Airbnb’s internal numbers could still suggest some concerns for investors and growing pains along the way.

The numbers come from my new book just out about Airbnb, The Airbnb Story: How Three Ordinary Guys Disrupted an Industry, Made Billions…and Created Plenty of Controversy.

In researching the book, and in the five or so years I have known Airbnb’s CEO Brian Chesky, one of the more interesting things I learned about this company—in addition to all the ways it almost never got off the ground, the singular amount of opposition it has incited, and the speed with which its founders had to learn how to run a large company—involves its business model itself. When you deliver a product based on other peoples’ assets and service, what you get is a network effect on steroids. The more people who stay at Airbnbs or use the service to rent out their home, the more valuable the platform becomes. And the company’s fixed costs are incredibly low.

In Airbnb’s case, since the very act of using its product involves travel, which is by definition migrating from one market to another, it also lends itself to cheap and easy cross-pollination (a Parisian tries Airbnb while visiting New York, likes it, realizes she has a spare room herself, and hangs an Airbnb shingle upon returning to Paris). It’s not just that it doesn’t have to build the rooms itself, Airbnb also doesn’t have to have a physical presence—offices, employees, etc.—to “launch” new markets. (Although it certainly does open offices, and by now has dozens offices and thousands of employees overseas). The net effect is that, according to sources familiar with the company, Airbnb has spent just $300 million of the roughly $3 billion in capital it has raised since its inception. By comparison, although not an apples to apples one, Uber was reportedly on track to lose $3 billion in 2016 alone.

(Related Book Excerpt: How Airbnb Found a Mission and a Brand)

This is why, when it eventually goes public, investor appetite for its IPO could be huge. Of course, Chesky still isn’t saying when that will be, and if anything hints that it could be a good while longer yet.

All of this is what helped propel the company to profitability last year, as Bloomberg reported (and as defined by earnings before interest, taxes, depreciation and amortization). According to sources, that profit was somewhere north of $100 million on $1.7 billion in revenues last year.

That’s projected to grow. The company is said to be forecasting EBITDA of $450 million on $2.8 billion in revenue for 2017. By 2020, Airbnb’s revenue is projected to be as much as $8.5 billion. Based on our latest rankings, that would place Airbnb at No. 325 on the Fortune 500. That would put the company just below Avis, and not much farther than Expedia. It would also be seven spots higher than News Corp., which, like Avis, has been around for far longer than eight years.

Of course, these are just projections, and importantly, they are for three years from now. But the company is still growing fast, even as it enters its ninth year. Airbnb’s main metric for user growth the company uses is “guest arrivals,” which is the number of times a traveler checks into an Airbnb listing. (One person who takes 3 trips a year would be counted as three “arrivals,” and four travelers in a group on the same trip in the same listing would count as four “arrivals.”) Last year, the annual figure grew from 40 million in 2015 to close to 80 million, almost doubling and helping push the cumulative figure to close to 160 million since the company’s founding.

Amazingly, that growth is not nearly as fast it was in Airbnb’s early years, when growth rates topped 300 and 400 percent.

That slower growth, though, may matter less now. The company is broadening its sources of revenue with its expansion into its Trips platform, a new menu of “experiences” it launched with great fanfare last November, along with other capabilities like restaurant reservations, events, and meetups. CEO Brian Chesky has said that the company plans to add more travel services to this menu—things like ground transportation, grocery delivery, and something involving flights. As he tells me in the book, he expects that revenue from accommodations as we know them today will eventually represent less than half of Airbnb’s overall revenue.

But again, this is all expectations, and Chesky loves little more than talking about the potential of Airbnb in the future. It’s also all somewhat ironic given that in Airbnb’s very formative days, he felt briefly that the service should be free—”like, no money,” as he told me. His cofounders Joe Gebbia and Nathan Blecharczyk helped convince him it could be a good business.

What’s more, the company has plenty of challenges, from legal battles to growing competition from a well-funded HomeAway to rare but headline-generating safety incidents.

But, as I report in the book, sources say that the company’s ten-year goal is to be the first online travel company with a market valuation of $100 billion. Marriott and Hilton’s market caps combined total $53 billion.

And if there’s one thing many have learned about this very disruptive company—especially the numerous investors who passed on investing in it in 2008 because its idea simply seemed way too risky and radical—it is not to underestimate it.

Update: An earlier version of this article said that Airbnb had lost less than $300 million since it was founded. In fact, the $300 million figure reflects how much money the company has spend of the total capital it has raised. The editors regret the error.

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