The shares of Shake Shack, a US burger restaurant chain, have dropped 8% in the after-hours trade after the company posted a fourth-quarter loss, for which it blamed a tax charge.

A decline of 6.3% was recorded in shares of Shake Shack to $43.98. Market analysts predicted a loss of 2 cents a share but the fast-food chain posted a loss of 5 cents a share in fourth quarter.

The company has reported a net loss of $1.4m for the period, as compared to $997,000 a year earlier.

Shake Shack Inc. shares started trading publicly in January, and fell in the extended session on Wednesday after the quarterly results fell short of Wall Street estimates.

A $1.1m tax charge related to company’s initial share offering was responsible for this loss. The firm has noted that same-store sales showed a 7.2% rise during the period ending December 31, 2014, beating the analyst expectations.

When the company made its US stock market debut in January this year, its shares surged 118%, which valued the company at more than $1.8bn.

Randy Garutti, Shake Shack's chief executive, said, "We are pleased with the strength of our fourth-quarter results and excited to begin our journey as a public company".

He added that Shake Shack has witnessed a seismic shift in people's understanding and expectations of food, and has helped lead the change in consumer behavior through its fast casual approach, in the last ten years.

Shake Shack was started in 2011 by a restaurateur Danny Meyer in New York City and presently it has 63 restaurants worldwide.

Besides, burgers and milkshakes, Shake Shack outlets also offer beer and wine along with a number of seasonal specials.

Shake Shack is part of a growing chain of so-called "fast casual" restaurants in the US. For example, Mexican restaurant Chipotle and sandwich chain Panera are competing with traditional fast-food firms like McDonalds for dominance.