I am looking to cash out my 401k. How would that affect me next tax season ?

[ColeenD3]

You will pay tax on the amount of your distribution. If you are under age 59.5, you will also pay a 10% penalty.

[SweetieJean]

There is no penalty if you left that job at age 55+.

Any increase in income can move you into a higher tax bracket; make more of any Social Security Income taxable; and/or lower or eliminate some deductions/credits. Also consider your State taxes.

Or, you can roll part or all of your distribution into a Traditional IRA within 60 days.  Otherwise, consider having taxes withheld when you take it,  in order to avoid and penalties/interest for underpayment of taxes.