Cambridge Bancorp, parent of Cambridge Trust Co., said it turned a $3.3 million profit in the first quarter compared to $3.1 million in the same period a year ago.

Earnings were boosted by net interest income of $11.5 million, a 9.2 percent increase over the prior year. Total loans outstanding increased by $18.1 million to $691 million since the end of 2011 and were up $84.7 million from March 31, 2011.

Net interest margin was 3.72 percent for the quarter compared to 3.89 percent in the same period a year ago. Non-interest expenses were $11.3 million, an $849,000 increase over the first quarter of last year.

The bank’s return on average assets was 1.02 percent for the quarter compared to 1.09 percent a year prior.

Total assets were $1.3 billion compared to $1.2 billion as of March 31, 2011.