Ideally you would have gotten a W-2G to report your winnings.

Here's where you enter Form W-2G (Certain Gambling Winnings) in TurboTax:

1. Open your return in TurboTax, if you aren't already in it. (To do this, sign in to TurboTax and select the Take me to my return button.)
2. In TurboTax, search for W2G (lower-case also works) and then select the "Jump to" link in the search results.
3. Answer Yes on the Gambling Winnings screen and follow the onscreen instructions to enter your W-2G.

After you've finished entering all of your gambling winnings, we'll ask about any losses you may have had. Losses can be deducted up to the amount you reported winning, but only if you itemize.

Gambling Losses

You may deduct gambling losses only if you itemize your deductions on Schedule A and kept a record of your winnings and losses. The amount of losses you deduct can't be more than the amount of gambling income you reported on your return. Claim your gambling losses up to the amount of winnings, as "Other Itemized Deductions.