Bill Ackman has lost $400 million on paper after buying Netflix stock in January.

Shivam

Bill Ackman's Pershing Square may be down $400 million after buying Netflix stock in January.

Three months ago, hedge fund XYZ's share of company ABC was valued at $1.1 billion; it is now worth close to $700 million.

For the past three months, hedge fund XYZ has seen its share of company ABC fall from $1.1 billion to close to $700 million.

The Bill Ackman bet on Netflix has potential to cost him $400 million.

Netflix shares dropped as much as 37 percent on Wednesday, after the video-streaming service reported slower growth in revenue last quarter.