The maximum amount someone can allocate to an elective 401(k) plan is $18,000 as of 2015, according to the Internal Revenue Service. The maximum amount is updated each year by the IRS to adjust to changes in the cost of living.
Someone who participates in multiple 401(k) plans must not exceed the maximum level across the multiple accounts. The IRS allows people over 50 to contribute additional funds through a "catch-up" contribution allowance, according to its website. As of 2015, the maximum someone can add for catch-up contributions is $6,000. This addition means someone 50 or older can contribute up to $24,000 total as of 2015.