A 401k plan is a retirement savings account offered by many employers that lets you save and invest a portion of your paycheck for the future. Contributions are made automatically from your salary, and you can choose to contribute on a pre-tax (traditional) or after-tax (Roth) basis, depending on your plan options. Many employers also offer a matching contribution, which is essentially free money toward your retirement. The money in a 401k grows over time through investments like stocks and bonds, and you typically can’t withdraw it without penalties until you reach retirement age. 401k plans often come with investment choices, tax advantages, and annual contribution limits set by the IRS.