"Is there an average percent that gets taken out by the IRS?"
I assume you are referring to the amount of tax due on the winnings - as you said, no taxes were withheld on your winnings - and the answer to that question is "NO."
Gambling winnings are just another example of "ordinary" income - like wages, pension income, interest, ordinary dividends, etc. - and will get taxed at "ordinary" tax rates which range all the way from 10% to 39.6%. How much that extra $4,000 will add to your tax bill depends entirely on your personal situation. Very roughly you might look at what tax bracket you were in last year and assuming nothing much has changed between this year and last, except for that extra $4,000 of income, you could apply that tax bracket rate to the $4,000.
Tom Young
