The maximum amount an individual can contribute to a 401(k) is $18,000 for the 2015 calendar year, according to About.com. Individuals 50 years of age and older may make additional catch-up contributions up to $6,000. These limits are set each year by the IRS.
The cap applies to all 401(k) accounts held by an individual for the current year; individuals with two or more accounts should track their contributions to ensure they do not contribute over the limit, according to About.com tax expert William Perez.
While contributions may be placed into a tax-deferred traditional 401(k), post-tax Roth 401(k) or combination of the two, matching employer contributions are always placed in the tax-deferred portion of the 401(k) and are limited to 25 percent of total salary.