Maybe.
Most people just enter their W2-g as income. Then they enter their losses upto, but not exceeding the amount of W2g winnings. But - and a big BUT - if your total itemized deductions are less than the standard deduction, then you do that instead and pay tax on the the W2G income... even if you put it all back and/or had a loss for the day.
It appears the IRS allows you to do session accounting. The Journal of Accountancy has an article about this.
