NEW YORK — Goldman Sachs’ earnings in the second quarter were flat with the same period a year ago, the investment bank reported Tuesday, largely due to poor performance in trading. The results still beat analysts’ forecasts.

The Wall Street firm earned $1.63 billion, basically unchanged from a year earlier. Because Goldman had fewer shares outstanding in the latest quarter versus a year earlier, its earnings per share increased to $3.95 from $3.72. That beat analysts’ estimates of $3.38 a share.

Goldman’s trading desks had a tough quarter, which reverberated throughout the firm’s results. The division that contains Goldman’s trading desks had revenue of $3.05 billion, down 17 percent.

The pain was particularly acute in Goldman’s fixed-income, currency and commodities division, which reported a 40 percent drop in revenue compared with a year earlier.

Goldman attributed the decline to a “challenging environment characterized by low levels of volatility, low client activity and generally difficult market-making conditions.”

Goldman and its rival Morgan Stanley, which will report its own results on Wednesday, make most of their money from trading securities and advising companies, and do not have large consumer banking divisions like JPMorgan Chase or Bank of America. If markets are quiet, as they were this past quarter, it tends to take a toll on Wall Street banks like Goldman and Morgan Stanley.

Investment banking revenue fell 3 percent from a year earlier, largely due to a drop in advisory fees.

Goldman’s difficulties were reflected in its return-on-equity ratio, a measurement of profitability, which fell to 8.7 percent. Typically a bank like Goldman tries to keep its return on equity above 10 percent.

Overall, firm-wide revenue fell to $7.89 billion compared to $7.93 billion a year earlier.