The the process for making contributions to IRAs differs from contributing to a 401k plan. For IRAs, the contributions are made from you to the account, typically held at a bank or other financial institution. These contributions do not affect your paycheck. Contributions to a 401k plan, on the other hand, come out of your paycheck and go directly into your 401k plan without you having to touch the money.
Since your employer knows exactly how much you have contributed to your 401k plan, the employer takes that into consideration when figuring how much taxable income you have for the year. For example, if your total salary equals $43,200, but you put $6,200 into your 401k plan, your employer would only report that you have $37,000 in income subject to federal income taxes because the money contributed to the 401k plan would already be accounted for on your W-2 form. As a result, you do not need to deduct the amount of your contribution on your taxes. With an IRA, since the contributions are made independently of your employer, you do have to report the contribution on your taxes so you can claim the tax deduction, assuming you are eligible.
Taking Money Out
When you withdraw money from either a 401k plan or IRA, the money is treated as taxable income that must be reported on your taxes the same way. However, the IRS requires that you report these amount separately. IRA distributions are reported on the "IRA Distributions" line of your tax return while you report 401k plan distributions on the "Pension and Annuities Distributions" line.
IRAs and 401k plans have different early withdrawal requirements to avoid the 10 percent early withdrawal tax penalty, imposed on most withdrawals before age 59-1/2, that must be reported when you file your income taxes. Some exceptions, such as medical expenses exceeding 7.5 percent of your adjusted gross income or suffering a permanent disability, apply to both. However, you can only avoid the early withdrawal penalty for college expenses or a first time home purchase with an IRA withdrawal. For only 401k plans, you can avoid the tax penalty if you retire after turning 55.
The IRS subjects both 401k plans and traditional IRAs to required minimum distributions starting at age 70-1/2 and imposes a 50 percent penalty on the amount not taken out from either a 401k plan or an IRA. However, the IRS allows an exception for 401k plans if the employee is still working, as long as she is not a 5 percent or greater owner in the business sponsoring the 401k plan. However, the tax treatment of required minimum distributions is the same.