If I win big, do I need to declare this income on my taxes?

A. Generally, you should probably declare all income on your tax return but you can discuss this is more detail with your accountant. If you plan on being a professional gambler, then you will need to start recording your playing time and results, session by session. The IRS has a guide for this: Guide 529 (available at the irs.gov website). For the best financial and tax advice, you should always discuss issues with your accountant or financial adviser.