IRA rollovers increased 7.3 percent in 2012 to reach $321.3 billion, Cerulli Associates analytics firm reports in its 11th annual Retirement Markets 2013: Data & Dynamics of Employer-Sponsored Plans report released Monday.

Rollovers topped $300 billion for the first time at the end of 2012 and are expected to continue to grow as baby boomers retire. The estimated total for 2013 is $357.5 billion.

“A large portion of the contributions roll over from defined contribution plans,” says Bing Waldert, director at Cerulli. “Participants do not necessarily roll over their assets immediately after leaving their employer. Some take action months or even years after their departure.”

Cerulli advises plan providers to inform participants that IRA accounts are available so that assets do not leave the provider if the participant decides to roll over. Immediately connecting with separated participants is essential in capturing assets, Cerulli says.

IRAs now account for 32.1 percent of retirement market assets, up from 27.6 percent in 2002 and now the largest segment of the market. The second-largest segment represented is public defined benefit plans, which are 23.4 percent of the market.