The ordinary income tax you must pay depends on what tax bracket you are in. If the tax and penalty add up to 40%, that means you are in the 28% and 33% tax brackets for your distribution averaging out to 30%. 10% is for the early withdrawal penalty.
As I assume you know, you get credit on your tax return for the 20% already withheld when you enter the withholding amount shown on your 1099-R into TurboTax.
