Wish it were that simple. See Notice 2015-21 at

https://www.irs.gov/pub/irs-drop/n-15-21.pdf

It’s a proposed revenue procedure, which six years later has not been issued in final form. But it starts out by agreeing with Tax Court opinions involving slot machines. If you have a compulsive-gambler client who actually tracks each “session” of play, there’s no reason not to rely on this.

“Gross income from a slot machine wagering transaction is determined on a session basis. See Shollenberger v. Commissioner, T.C. Memo 2009-306 (2009); LaPlante v. Commissioner, T.C. Memo. 2009-226 (2009). Determining whether a series of wagers is a “session” requires analyzing the relevant facts and circumstances and can present practical difficulties. Shollenberger, supra. . . .

“Session of Play. A session of play begins when a patron places the first wager on a particular type of game and ends when the same patron completes his or her last wager on the same type of game before the end of the same calendar day. For purposes of this section, the time is determined by the time zone of the location where the patron places the wager. A session of play is always determined with reference to a calendar day (24-hour period from 12:00 a.m. through 11:59 p.m.) and ends no later than the end of that calendar day.”

There are obsessive gamblers, and then there are obsessive tax preparers who want every number on an information return to match a number on the 1040.  It isn't going to happen, in these situations.  Tell your client to stop gambling, but to call you if IRS sends a CP-2000 (which they aren't going to do for a $1,000 discrepancy in income).  And then, send IRS a copy of the attachment you filed with the return.