The social network on Thursday said that it posted $3 billion in revenue in 2018, topping the $2.4 billion the company posted in its 2017 fiscal year. And despite losing $108 million in the prior year, Twitter was able to nab $1.2 billion in profit during its 2018 fiscal year. In fourth-quarter metrics, which included revenue of $909 million and 31 cents earnings per share, Twitter beat analyst expectations.

Still, in early trading on Thursday morning, Twitter shares (TWTR) are tumbling. As of this writing, Twitter’s pre-market share price is at $31.62, down 7.44% against its Wednesday closing share price of $34.16.

Investors appear to be concerned that Twitter is seemingly expecting a slightly less successful 2019. In its guidance, the company offered a revenue range of $715 million to $775 million against analyst consensus of $764.9 million, according to Refinitiv data published by CNBC. Twitter is also anticipating operating income during the quarter of $5 million to $35 million—well below the $74.9 million operating income Twitter posted during the same period last year.

In its earnings release, Twitter said that it anticipates increasing its operating expenses by 20% this year to address its “existing priorities of health, conversation, revenue product and sales, and platform.” Investors aren’t typically so keen on such big bumps in spending.

All of that came alongside Twitter’s announcement on Thursday that it’s changing its user metrics in earnings releases. The company will do away with monthly active users after its first quarter release and instead turn to “monetizable daily active users” (mDAU).

In a statement, Twitter said that an mDAU is a user who is accessing its service “on any given day” and is able to be shown ads. The move effectively removes users who are not shown ads and therefore not able to generate revenue for the company.

“Our mDAU are not comparable to current disclosures from other companies, many of whom share a more expansive metric that includes people who are not seeing ad,” Twitter said.

The move, however, sheds light on how many of Twitter’s users are actually “monetizable.” And it might have surprised some investors.

According to the company, it now has 321 million monthly active users—a metric used often by social media companies to evaluate user growth. That’s down slightly from 330 million at the end of 2017. Out of that 321 million, 126 million are mDAU, or able to generate revenue for the company. That metric is up from 103 million in 2016 and 115 million in 2017.

In its earnings release, Twitter was quick to note that the new user disclosures will not impact its relationship with advertisers or the information they get before deciding to advertise on the social network.