An early withdraw from your 401k plan is any withdraw that you make before the age of 59½ years of age. The penalties you will have to pay often depend on the specifications of your company’s 401k plan, but there are some common penalties that apply in most cases.

Calculating 401K early withdrawal penalties involves looking at several different costs that you may incur for taking your money out before it is time.
If you plan to withdraw money early, here are the penalties you will need to take into consideration:
The first penalty you will be assessed is federal tax.
To calculate the federal taxes you will owe for taking money out of your 401K early, you first need to determine your personal federal income tax rate. You will then need to apply this rate to the amount that you are withdrawing. For instance, if your federal income tax rate is 28 percent and you plan to withdraw $10,000 from your 401k plan early, you will have to pay $2,800 in taxes.
You may argue that when you take your money out of your 401K at retirement that you'd have to pay taxes too. However, in many cases, people's income (and thus, their tax bracket) falls when they enter retirement, so there is a chance the taxes on the 401k withdrawal would have been less if you'd waited to withdraw the money until you were at least 59½.
The second penalty you will have to consider is the state tax due on this early withdrawal.
In addition to the taxes on your early withdrawal, you will also be required to pay a general tax penalty on the monies that you withdraw early from your 401k account. This is above and beyond the taxes you will be required to pay at the state and federal levels.
So, now you know the penalties to include when calculating 401K early withdrawal penalties. This will help you make a more informed decision about whether or not you want to make an early withdrawal.