20% is the required minimum federal tax withholding on any rollover-eligible distribution from a 401(k). It is not necessarily the incremental tax liability you will incur from receiving the distribution. Your actual tax liability is determined when you prepare your tax return and could be substantially less or substantially more, so you'll want to estimate your actual tax liability and specify a higher percentage for withholding if needed to avoid an underpayment penalty. If the minimum 20% withholding is more than necessary, any excess tax withholding becomes part of your tax refund after you file your tax return.
Georgia does not have a minimum withholding requirement. You can specify the amount of Georgia tax to withhold. The top Georgia tax bracket is 5.75%, so it might make sense to have up to 6% withheld for Georgia taxes. (Many payers of such distributions require tax withholding to be specified in whole percentage points.)
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