The company said it is in part because more people are using Facebook on mobile devices, where it shows a very small number of ads. It implies that Facebook has room to grow in the still-nascent mobile advertising space.
Facebook said it saw that trend in the first quarter, and that has continued in the current quarter.
The company made the disclosure Wednesday in and amended S-1 regulatory filing.
The changes came after executives met with prospective investors in New York and Boston ahead of its initial public offering.
Facebook added three paragraphs related to mobile usage to its filing. The additions were likely in response to questions from investors.