What US tax laws are concerned for winning a lottery or gambling overseas?

Gambling winnings are taxable as income, but you may also deduct costs associated with your winnings.

But how much?

That depends on your rate at the time.

I mean percentage. Would it be about half? 40%?

Owed to the irs.

The US uses a progressive taxation rate so without a fairly exact number, it is effectively impossible to say.

It is taxable as regular income. If it bumps you to a higher tax category you will pay more.

Once again, i attempted to answer this question and was logged off. Fluther must have a virus. now would be an excellent time to call the IRS and ask your question. you do not have to give your name or any personal information about yourself.

US Citizens are taxed on world wide income, so yes, you have to report your gambling winnings. BUT you can also deduct your losses (with proper documentation!) to the extent of your winnings.