This has been discussed in other threads, but there doesn't seem to be total agreement on the answer.

If your total income including poker is less than the threshold (I believe 9350 this year) do you have to report/pay taxes on poker income?

If you are self-employed (professional player) and made more than $400 of SE income, you must file. Otherwise, if you're under $9,350, you need not file.

Keep in mind that this $9350 threshold is likely on gross, rather than net; if you are an amateur poker player who made $1k via $11k in winning sessions and $10k in losing sessions and that's your only income, I believe you have to file.

Correct. $9,350 is the top line figure.

How serious is the gross/net thing? I've talked to people who just filed their net as gambling winnings and didn't get into trouble.

Pretty serious IMO. It can have a significant impact on the total tax you owe. Just filing one's net is a direct violation of the tax code and it's not something that individual taxpayers have the right to do, in any sense. Possibly an audit flag, too, if someone filed gambling winnings with no gambling losses.

What repulse said.

As with anything else involved in filing your taxes you can do it wrong (either on purpose or by mistake) and if the IRS doesn't question it for some reason (an audit or otherwise) then it doesn't matter. Once they do this is going to be discovered quickly. It's also something that will be apparent quickly if they look at your gambling winnings.

A few years ago I got a letter after filing my return asking for W2Gs to substantiate my gambling winnings. I was able to easily explain not having W2Gs because these were "the total of my winning sessions from my poker journal" and that they were partially offset by the losing sessions on schedule A. If questioned about a net amount any explanation about a non-trivial amount of winnings is going to look suspicous because everyone has losing sessions. You aren't obligated to deduct losing sessions, but that you didn't makes it look like you probably incorrectly netted. If they decide to dig deeper it won't be fun.

Note that this $9,350 only applies for people filing as single, non-dependents.

For dependents, the actual number is lower.