In 2015, you are allowed to contribute up to $18,000 of your income to a 401(k) and an additional $6,000 if you are over 50.
The money is pretax, a direct salary deduction, and stated on the W-2 issued by the employer. A 401(k) as well as 403(b) and 457 are 'qualified' employer sponsored retirement plans, sometimes employers offer matching contributions up to a percentage of your salary.
