If your U.S. losses are less than your winnings, you will get a partial refund. I won some jackpots at a casino on Lake Michigan this year. We have a house in Indiana, but over the years we have claimed California as our residence. A Most states tax income earned in their state, regardless of residence, and most states offer a credit to their residents for taxes paid to other states. This is true in your case.
Most states allow the deduction of gaming losses.
If you end up paying Indiana tax, that amount can be credited to the amount of tax on your California return. In February of 1998, in a case involving an unemployed gambler who failed to file timely returns for two years and kept no records, the Tax Court ruled that the gambler could not deduct unsubstantiated gambling losses. In addition the Tax Court upheld the IRS which had levied additional amounts for failure to file on time and for the accuracy-related negligence penalty. In other words, they threw the book at this gambler, who actually told the court that although he maintained a gambling log for one of the years in question, it was not accurate because it was too time-consuming to make it precise. If you are collecting W2-Gs and not keeping accurate records, this very well could be in your future.