How many hours of overtime can I work before they tax me more?

There is no set amount of hours of overtime that you have to work before you are taxed more. That is not how taxes work. Overtime wages are taxed at the same rate as your regular wage bracket. You are taxed more if your earnings put you into the next bracket. So, no set number of hours puts you into a higher bracket, it depends on your income.

For example, if you make $40,000 annually, you are taxed at 12%. This tax bracket goes up to $44,725, so if you work enough hours that your income bumps to anything above that, you are then taxed more. It is important to note that with taxes, you would only be taxed more on any income that goes over $44,725. You wouldn't be taxed more on any wages under $44,725.