Profits are crucial to the growth of any company, but some of the biggest names in business today have yet to make money.

Publicly-listed companies like electric carmaker Tesla and music streaming firm Spotify make billions in losses.

Likewise, ride-hailing firm Uber lost $4.5 billion last year, but is gearing up for a highly anticipated public listing that will likely take place next year.

Investors are not put off by unprofitable companies. In fact, the proportion of companies reporting losses before going public in the United States is at its highest since the dotcom boom in 2000.

Last year, 76 percent of the companies that listed were unprofitable in the year before their initial public offerings, according to data compiled by Jay Ritter, a professor at the University of Florida's Warrington College of Business.

That's lower than the 81 percent recorded in 2000, but still far higher than the four-decade average of 38 percent.

The rapid growth of the tech sector is one reason why investors are willing to put their money into unprofitable companies, since many shareholders value growth and tend to be more comfortable even if firms aren't making huge margins.

Ritter's data showed that of the companies that went public last year, just 17 percent of tech companies were profitable compared with 43 percent of non-tech companies.