Tax Consequences on 401(k)

Most 401(k) contributions are on a pre-tax basis. Starting in the 2006 tax year employees can either contribute on a pre-tax basis or opt to utilize the Roth 401(k) provisions to contribute on an after tax basis and have similar tax effects of a Roth IRA. However, in order to do so, the plan sponsor must amend the plan to make those options available. With either pre-tax or after tax contributions, earnings from investments in a 401(k) account (in the form of interest, dividends, or capital gains) are not taxable events. The resulting compound interest without taxation can be a major benefit of the 401(k) plan over long periods of time.

For pre-tax contributions, the employee does not pay federal income tax on the amount of current income that he or she defers to a 401(k) account. For example, a worker who earns $50,000 in a particular year and defers $3,000 into a 401(k) account that year only recognizes $47,000 in income on that year's tax return. Currently this would represent a near term $750 savings in taxes for a single worker, assuming the worker remained in the 25% marginal tax bracket and there were no other adjustments (e.g. deductions). The employee ultimately pays taxes on the money as he or she withdraws the funds, generally during retirement. The character of any gains (including tax favored capital gains) are transformed into "ordinary income" at the time the money is withdrawn.

For after tax contributions to a designated Roth account (Roth 401(k)), qualified distributions can be made tax free. To qualify, distributions must be made more than 5 years after the first designated Roth contributions and not before the year in which the account owner turns age 59 and a half, unless an exception applies as detailed in IRS code section 72(t). In the case of designated Roth contributions, the contributions being made on an after tax basis means that the taxable income in the year of contribution is not decreased as it is with pre-tax contributions. Roth contributions are irrevocable and cannot be converted to pre-tax contributions at a later date. Administratively Roth contributions must be made to a separate account, and records must be kept that distinguish the amount of contribution that are to receive Roth treatment.