Shares of Potbelly Corp., the hot-sandwich maker that went public nine months ago, dropped in late trading Wednesday after its annual profit forecast and quarterly sales trailed analysts’ estimates.

The shares were down 16 percent at $12.25 at 6 p.m. in New York, after tumbling as much as 20 percent after the close. They had fallen 40 percent this year through the end of regular trading Wednesday, while the Standard & Poor’s 500 Index gained 6.7 percent.

Adjusted profit this year will be as much as 21 cents a share, the Chicago-based company said in a statement. Analysts estimated 34 cents a share, the average of four projections compiled by Bloomberg. Preliminary second-quarter revenue rose 6.9 percent to about $83.6 million, while analysts estimated $86.7 million.

Potbelly, which has more than 300 locations in the U.S., has been trying to boost sales with store openings and by selling new lower-calorie flatbread sandwiches. The chain plans to release full second-quarter results on Aug. 5.