Elective deferrals to a 401k are not taxed at the time of the deferral so any contributions that you made to the 401k are tax free.
When you make a distribution from a 401k the plan administrator is required to withhold 20% of the distribution for federal taxes. The distribution is entered on your tax return as ordinary income and taxed at your current tax rate. The taxes withheld from the distribution are entered on your tax return as a tax payment.
You will receive a Form 1099-R for the distribution in January of the year following the distribution. You are required to enter the information on the 1099-R on your federal tax return.
