Century Bancorp boosted profits last year, increasing net income 9 percent to $21.9 million for the year ended Dec. 31.

The Medford-based holding company for Century Bank also increased its total assets 5.6 percent to $3.6 billion during that period and boosted net interest income 8.7 percent to $66.2 million in 2014, an increase driven primarily by an increase in average earning assets.

The company’s net interest margin inched up to 2.22 percent in 2014 from 2.21 percent the previous year, the result of a decrease in rates paid on deposits and borrowed funds. Century’s interest expenses also increased slightly along with an increase in deposit balances, the company said in a statement

Century Bancorp decreased its provision for loan losses for the year, to $2.1 million from $2.7 million in 2013. The allowance for loan losses totaled $22.3 million, or 1.68 percent of loans outstanding at Dec. 31, compared with $20.9 million and 1.66 percent in the year-ago period. That increase was due to an increase in the size of the loan portfolio. Non-performing assets increased to $4.1 million at year-end 2014 from $2.5 million at year-end 2013.

Total equity stood at $192.5 million at the end of 2014, compared with $176.5 million the prior year. Equity increased largely as a result of earnings, but that was offset by an increase in additional pension liability, and dividends paid. That was offset somewhat by a decrease in unrealized losses on securities available-for-sale and securities transferred from available-for-sale to held-to-maturity. During the third quarter of 2013, $987 million of securities available-for-sale with unrealized losses of $25.3 million were transferred to securities held-to-maturity in response to rising interest rates.

The company’s board of directors voted a regular quarterly dividend of 12 cents per share on the company’s Class A common stock, and 6 cents per share on its Class B common stock. The dividends will be paid Feb. 17 to stockholders of record on Feb. 2.