Yes you can open and contribute to more than one 401k at the same time. For example, in accordance with IRS regulations, you could contribute to your day job 401k (regular employer 401k) and your self-employed 401k (commonly called Solo 401k, Individual 401k or Solo k) at the same time. See IRC Sec. 402(g)
Basically, if the individual is an employee at one company, and operates Solo 401k Plan for his or her side business, he or she is subject to one IRC Sec. 402(g) limit. Therefore, he or she must aggregate the deferrals in both plans and remain under the maximum 402(g) limit ($50,000 for 2012, plus $5,500 catch-up contribution if eligible–you are age 50 or older in 2012).
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Jerry has two (2) jobs: Job 1 as Computer Engineer at Apple (his full time job), and Job 2 as Real Estate Agent for Keller Williams Realty (his owner-only business / part time job). For 2012, Jerry is deferring $10,000 in Apple’s 401k plan to maximize Apple’s 401k employer match. Jerry, therefore, could open Solo 401k for his 2nd Job and defer an additional $40,000 to it for 2012, provided he has the self-employment income.
