I cashed out part of my 401K (20K) after leaving my job this year. 20% was withheld for taxes, as well as a 10% penalty. My question is: After filing my tax return in 2017, is there an additional percentage in taxes I should expect to pay? Or will the 20% already withheld cover that?
It depends on how much other income you have. The 401k withdrawal is added to your other income and taxed at whatever your marginal tax rate is. If your marginal tax rate is more than 20%, then you will owe more income tax.