Bill Ackman's fund has had a terrible August

Thomson Reuters

William Ackman, founder and CEO of hedge fund Pershing Square Capital Management, speaks to the audience about Herbalife company in New York

We knew Pershing Square Holdings' performance had faltered in August. Now we know by how much.

The publicly-traded vehicle led by Bill Ackman wiped out all of its gains for the year and fell into the red in August.

According to an update, the fund fell 13.1% during the month of August and was down 4.3% for the year as of Tuesday.

It's been a volatile week in the markets. With Thursday's close, the S&P is now positive for the week having tanked earlier in the week.

Ackman holds large positions in a handful of publicly-traded companies. In an investor update, he said that Pershing wouldn't be forced to sell out of those stocks.

It's possible Ackman could have made back some of those losses. The next update comes out next week.

Pershing Square Holdings had been up 10.1% through the end of July.

Ackman wrote that all gains for the year had been erased because of "significant volatility in the investment markets over the past few weeks, largely driven by the decline of the Chinese stock markets, and the fear that slowing growth in China will have repercussions for businesses around the world."

In 2014, Ackman was one of the best-performing hedge fund managers, gaining about 40% compared to the S&P 500's 13% rise.